The present paper is concerned with inheritance of the development of lateral florets in crosses of two-rowed forms of barley of the distichon type with the six-rowed forms of types vulgare and brachyurum.
The character can be employed for identification of true hybrids as early as in the F₁ generation in crosses of two and six-rowed forms when the two-rowed character is dominant. Unsuccessful crosses can thus be eliminated in time. The character can also be useful for the determination of linkage ratios in higher hybrid generations.
1. Heredity of the development of lateral florets in spikelets of barley spike was investigated during hybridization of two-rowed and six-rowed forms by means of the method for continually variable characters.
2. The results obtained indicate that in the manifestation of the character, nuclear factors of two types take part, i. e. the more numerous factors of lesser effect, (here apparently also belong the pleiotropic effects of factors for other characters), and the less numerous factors of greater effect which appear to be fairly independent of the alleles for the number of rows in the spike.
3. It seems that extranuclear factors participate in addition to the nuclear as suggested by the inequality of reciprocal crosses in the same combination.
4. The modifiability of the degree of character manifestation due to external factors is great in hybrid plants.

The present investigations were designed to explain the physiological causes of the increase in metabolism and growth in the shrubRhus aromatica L. after pruning. The determination of the concentration of the different forms of nitrogen compounds, of sugars, organic acids, phosphorus and also of the dry weight of the leaves from the pruned and from the control plants at different times during 24 hours, showed that the positive influence of the pruning on plants is due to the increase of the amplitude and of the synthesis and transport of organic substances from the leaves as well as of the transport of the minerals and water into the leaves.

1. The differences in the dynamics of the origin and further development of the water saturation deficit (WSD) in leaves of different age from 100- to 120-day-old plants of fodder cabbage and rape were investigated.
2. WSD in leaves of different age detached from plants and wilting without water supply develops most quickly in young and most slowly in old leaves. This is in basic agreement with differences in transpiration rate.
3. When entire plants are cut off, leaves of different age wilt at the same rate. In the later phases of wilting, (i.e. at a WSD value of over 20 to 30%) slightly higher WSD values were found in old leaves.
4. During slow wilting of plantsin situ, induced by decreasing soil moisture, a definite preference of young leaves in water supply was determined commencing from medium WSD values, i.e. on an average from 8 to 20%. During total lack of water in the plant, old and adult leaves wilt markedly and die off; the WSD of young leaves remains for a long time at comparatively low values.
5. In the observed preference of young leaves, the translocation of water to young leaves from the wilting older leaves takes a part.

Leaf cells of healthy cucumber and cucumber infected with Cucumber virus 4 were studied living and fixed, using optical and electron microscopy. Under the electron microscope the infected leaves displayed changes in the structure of the ergastoplasm, Golgi apparatus, mitochondria, bodies with an osmiophil matrix and chloroplasts. The chloroplasts exhibit symptoms of fatty degeneration which affects above all the lamellar systems of grana and intergrana. Weakly osmiophil globules, abundant in damaged chloroplasts, are probably formed through degeneration of grana. Chloroplasts of infected plants resemble some transitional stages of plastids observed during chromoplast formation. The problems of localization of viruses in the cell and degeneration are discussed.

From photoperiodic experiments and an anatomic study of the shoot apex in the facultative short-day plantsPerilla ocimoides L. it was shown in all cases that gibberellic acid (GA) application did not accelerate flower induction. Between the development grades 2 and 4, GA caused a certain temporary acceleration which, however, completely equalised in a short period and plants of both variants SD and SD+GA flowered at the same time. Long day plants (LDand LD+GA) also flowered simultaneously with a certain delay. GA caused the total length of the plant to increase in both cases by more than a double, while preserving practically the same number of leaf pairs in variants under the same photoperiodic regime.

1. Suppressors were found in reciprocal crosses of some varieties of barley for the manifestation of recessive and dominant alternatives of the following characters: number of rows of the spike, presence or absence of glumes, character of awns and formation of the spike basis.
2. A proof of the existence of suppressors is presented merely statistically on the basis of segregation ratios in the F₂ generation, in the total F₃ generation and in the individual segregating progenies of plants from the F₂ generation and in the back crosses.
3. It was confirmed that the inheritance of the characters investigated is independent in spite of the fact that the segregation ratios are complicated by the participation of suppressors.
4. Separated cultivation of individual progenies from hybrid seeds formed on the mother plant was shown to be very suitable and efficient in hybridization experiments of this type.
5. The significance of the participation of the suppressors in the inheritance of the characters studied is pointed out with respect to the practical breeding of barley.

The indirect influence of irradiation on the production of anthocyanins in the blossoms of red balsam (Impatiens balsamina L.) was investigated. After 18 hrs. of swelling, seeds were irradiated with 4560 r and then changes in the anthocyanin content of blossoms were examined. In X₀ three out of four lines tested displayed a marked increase in anthocyanin content by 18%, 18% and 29%. In X₁ the quantitative content of anthocyanins either equalled that of the controls or was lower, in X₂ a significant decrease in anthocyanin content in all the lines was observed. We are apparently dealing here with a physiological effect of the type of "prolonged modifications".
In X₁ several plants with pink flowers appeared (3.4%). It is assumed that this is not due to a segregation caused by heterozygous material (the controls did not show this effect) but rather to a recessive mutation brought about by irradiation, which became apparent only in X₁.

A method is described for the application of the dry weight increment technique of photosynthesis measurement to plants with narrow leaf-blades (e.g. Festuca, Stipa etc.). A sample of leaf tissue is represented by the area of a frame filled with leaf segments placed side by side. The leaf segments 26 mm. in length are cut out from the leaves with a special punch; their number in the sample must be determined empirically for each plant species. In connection with this problem the authors describe the relationship between the intensity of photosynthesis and the number of segments in a sample.
The accuracy of the indirect determination of dry weight increment with the aid of control samples is maximally ±1% for ten estimations and 5% probability, which makes it possible to determine photosynthesis with an accuracy of ±10% when the assumed dry weight increment is 10%.

After the application of a fractionated X-ray dose toArabidopsis thaliana L. (Heynh.) plants, chlorine type mutations (simple recessive -cc- as compared with the normal type -CC-) characterised by changed proportions of chlorophyll colouring matter as well as a decreased leaf area, retarded development in the initial phase and a substantially longer vegetative cycle, make themselves apparent. In the course of future generations, however, these characteristics change in the direction of normal types and stabilise in the sixth generation. A genetical and cytological evaluation of this manifestation showed that this mutation is connected with lesser number of plastids in the assimilative tissues. This number remains standard in all generations of the chlorine type, but on the other hand, the size of the plastids increases.

If the flowers for experiment were separated from the plants one day before pollination and incubated in water at a temperature of 25° C, pollen tube growth in the pistils made itself apparent during the following three days in the glucose and fructose level. On the first day after pollination the amount of these sugars in the apical style parts was higher in non-pollinated flowers, while on the other hand, in most cases it was lower in the basal sections and ovaries than in the corresponding parts of pollinated flowers. During the next two days there was a greater loss of both carbohydrates where pollination, particularly allogamy, occurred, so that after the third day the glucose and fructose level was highest in the non-pollinated pistils and lowest after compatible pollination. This decrease was most pronounced in the ovaries even though the compatible tubes had not yet penetrated into them. In experiments in which the flowers were left on plants cultivated under field conditions, a decrease in the glucose and fructose content of their pistils had not occurred even 80 hours after compatible pollination.
From these facts the following conclusions can be drawn: The growth of the tubes through the styles causes an increased inflow of carbohydrates into the whole pistils. Both compatible and incompatible tubes use sugars from the style tissue. Both these phenomena are more intense after allogamy than in the case of incompatible autogamy. In view of the fact that compatible tubes grew normally through the styles even with a lowered glucose and fructose level, an absolute rise in the content of these sugars in the pistils is not necessary for tube growth.
The proportion of glucose/fructose in pollinated styles changes in favour of glucose. The value of this quotient rises both in the apical and basal style parts mainly, however, after compatible pollination. This phenomena is in agreement with the previous hypothesis (TUPý 1959, 1960), according to which, in the respiratory process, pollen tubes consume mainly sucrose and from this, primarily its fructofuranose component.

Proof is given in this paper that dwarfing of wheat, which occurs in several regions of Czechoslovakia, is a virus infection. The virus was transmitted by means of naturally infected imagos of the leaf-hopperPsammotettix alienus DAHLB. to spring wheat and spring barley. It was also found that it is transmissible to a high degree by larvae grown from eggs which are then artificially infected at the source of infection. An attempt to transmit the virus by means of the aphidsBhopalosiphon oxycanthae (SCHRANK.) andSitobium granarium (KIRBY) MORDV. was negative. Nor was it possible to transmit it by soil, wheat grains or by mechanical inoculation with sap from diseased plants.
The Russian mosaic virus of winter wheat would seem, in view of its vector, to be the most closely related to the wheat dwarf virus. It differs, however as regards the symptoms produced on the host cereals, by having a different vector and by the absence of inclusions in the cytoplasm of infected plants. These facts indicate that we are probably dealing with a new virus, which has not previously been described.

Seven strains of the clover phyllody virus originating from different localities in Slovakia were transmitted by means of the leafhopperEuscelis plebejus (Fallen) toTrifolium repens L.,T. pratense L.,T. hybridum L.,Senecio vulgaris L.,Taraxacum officinale WEB.,Chrysanthemum carinatum SCHOUSB.,Vinca rosea L. andThlaspi arvense L. Thus the ability ofE. plebejus to transmit the clover phyllody virus occurring in Slovakia was confirmed. The incubation (latent) period of virus in the vector lasted about a month and the percentage of leafhoppers which became viruliferous amounted to 30-60%. The importance of susceptible weeds in the circulation of the clover phyllody virus in nature is pointed out and the symptoms of disease caused by the individual virus strains in the plants tested are described.

Photoperiodic experiments with the spring wheat Niva were undertaken to investigate the course of photoperiodic sensitivity and localization of the dhotoperiodic reaction in the ontogeny of plants. The long-day plant used, however, was not amenable to detecting a period during which a shortened day would be completely devoid of effect on the rate of development. Some data indicate, however, that a period of increased photoperiodic sensitivity can be defined which would correspond to the period of photoperiodic reaction of short-day plants. The results also seem to indicate that this period does not terminate abruptly but gradually passes over into the ensuing period when the day length affects the rate of development solely through photosynthesis. This effect is well marked when such indicators as the shoot apex development and earing are employed. The existence of this transition period at the end of the period of increased photoperiodic sensitivity and its connection with the shoot apex phase from initiation of spikelets to initiation of stamens must be verified by a long-term experiment under strictly controled conditions.
Among the criteria used to examine the course of photoperiodic sensitivity earing appeared to be most suitable as it yielded curves with definite, more or less marked breaks; the investigation of abnormities (in a classical arrangement), too, proved to be of value, as they indicate interference with the relationship between growth and development. Orientation data were also obtained by measuring plant size in a classical arrangement of the experiment. Analyses of the developmental phase of the shoot apex proved to be of least value in the experiments described here.

The foliar absorption and subsequent distribution of sodium, chlorine, calcium and zinc in one-year-old rooted cuttings ofForsythia intermedia ZABEL, and root absorption of phosphorus byTaxus cuspidata SIEB. and Zucc, was established. The percentage of the applied nutrient translocated out of the treated leaf was used as a criterion of mobility. Sodium and chlorine were found to be mobile, calcium immobile, and zinc slightly mobile. Less than one percent of the phosphorus applied to the shoots of both actively growing and semi-dormantTaxus cuspidata plants was recovered in the roots after a 12-day absorption-transport period. Six percent of the total phosphorus recovered in the tops was derived from a single soil application of a water soluble fertilizer (10-52-17) after 12 days, although, less than. 0.5 percent of the applied fertilizer phosphorus was absorbed.

As the species hybridSalvia němecii (= S. nutans x S. jurišićii) is highly fertile, genetic analysis of the segregating F2 generation has been carried out. In 238 plants of F2 the following leaf characters were investigated: type of the vascular bundle course in the petiole, the ratio of the petiole to leaf blade length, the ratio of the length of the leaf blade to the breadth, and the segmentation of the leaves, i.e. ratio between an ideal contour surface and the actual surface of the leaf blade. All these characteristics were compared with those of the original parental species as well as of the F1 generation. It was found that:
1. Type II of vascular bundle course has simple dominance over type III (segregating ratiol72 : 66, X²(1) = 0.94, P = 0.35).
2. All morphological characteristics of the leaves behave as though governed by polygenic systems. The segregation in F₂ is always very wide and the extreme segregants exceed the values present in both parental species.
3. The type of vascular bundle course in the petiole is inherited independently of the morphological signs of the leaves. There is practically no correlation between vascular bundle type and any of the morphological ratio indices.
4. Between the morphological characters, on the other hand, there are significant correlations, especially between the length of the petiole and segmentation of the leaf (r = 0.31), and between the segmentation and the length-breadth ratio (r = -0.42). Therefore, some of the polygenes concerned may be linked together, i.e. localized in the same chromosome, but most of them are transferred independently.

1. Photoperiodic experiments with the effect of short day during vernalization of winter wheat under field conditions have shown that the short day enhances development if applied during vernalization. Short day applied after vernalization prolonged the development.
2. At low intensity artificial illumination and under optimal vernalization temperatures vernalization proceeds the faster the longer the illumination. On increasing illumination intensity differences between the effect of short and long day are obliterated. Vernalization in the dark takes place only if saccharides are added.
3. It is assumed that even in green plants the accumulation of a certain amount of ergastic material, particularly saccharides, represents one of the conditions of vernalization. This accumulation may be achieved by longer illumination (under conditions of vernalization temperature and low illumination intensity), i.e. by a direct photosynthetic effect, or else by short day (under field conditions) causing a specific, photoperiodically controlled growth reaction which inhibits growth. When vernalization proceeds in the dark saccharides must be supplied.

The extent of material that had to be examined in the cytological evaluation of 40 varieties of the Czechoslovak basic assortment of pears made it necessary to work out a new, rapid method of investigation.
This method makes it possible to obtain permanent sections from about 1800 anthers within three days. During the first day, a total of three series can be imbedded in paraffin wax and each of these may contain about 600 anthers. There is sufficient time during the second day to section the three series and place the sections in gallocyanin where they are left overnight. On the following day, the sections containing about 1800 anthers are imbedded in Canadian balsam.
This method can be used with all plants having anthers sufficiently large for extirpation during the period of cell-division in the pollen mother-cells.

The aim of this work was to establish under what conditions the water deficit values obtained byStocker's (1929) method can be considered to be those for actual water deficits. It was found that the water intake of detached leaves is not necessarily due only to incomplete saturation of the leaf tissues with water, but that in young leaves it is caused to a great extent by their extension growth. Thus, water deficit in the sense ofStocker's definition is not merely a simple physiological state of incomplete saturation of the tissues, but is expressed by the sum of the need for water to achieve the greatest possible saturation of the tissues and the need for water in the normal course of the extension growth of cells.

The authors studied the effect of the application of humus substances to the leaves ofBegonia semperflorens Link etOtto. For spraying they ušed a dialysed extract of garden soil containing sodium humate with admixture of fulvic acid in total concentration of 300 mg/l. Doses of 2 ml. were applied twice a week during the period of the main growth phase.
It was found that humus substances applied to the leaves cause a leng-thening of plant organs and increase of their fresh and dry weights. The chloro-phyll content and the amount of expired carbon dioxide are increased. The final result depends on the time when spraying was carried out and on the concentration used. It can be assumed that these effects are the result of direct influence by the humus substances and are not due to the action of stimulated soil or root microflora nor to improvement of the physicochemical character of the soil environment.
In conclusion we may say that humus substances applied to the leaves cause lengthening of the plant organs and increase in their fresh and dry weights. Chlorophyll content and the amount of expired carbon dioxide are also increased. The final effeet depends on the period of spraying and on the concentration used. In view of the fact that these effects do not differ from the effects caused by humus substances given as a part of root nutrition, we may assume that they are the result of direct action of humus substances and not of the action of stimulated soil or root microflora, nor to the improve-ment of physical or physico-chemical character of the soil environment.
A prerequisite for the practical utilization of humus sprays is, however, the extension of experiments to a greaternumber of plant species, the determination of their sensitivity, suitable concentrations of the solutions and the most suitable time of application.

In addition to the oat sterile-dwarf virus (OSDV) as the main agent causing grave damage to cereal crops in the Bohemian-Moravian Highlands during 1954-56, when the disease reached catastrophic proportions, it was found that wheat striate virus (WSV) also played a part. Symptomatological study showed that there are characteristic differences between the effect of WSV on the host plants and that of OSDV. Similarly to OSDV, however, WSV is specifically spread by the leafhopperCalligypona pellucida Fabr. Following long-term individual testing of vectors taken from localities infested with OSDV and WSV, four groups of insects were distinguished according to their pathogenic effects on cereal crops: 1. nonpathogenic, 2. producing OSDV symptoms, 3. producing WSV symptoms, 4. producing for the most part OSDV symptoms, but occasionally WSV or symptoms characteristic for both viruses simultaneously. WSV is persistent in its vector and is transferred byC. pellucida larvae at different stages of development and by imagos of both sexes. WSV tends to be transferred less regularly than OSDV. Considerable differences in efficiency of carrying WSV are to be found between individual leafhoppers, so that it is possible to assume the existence of races with varying efficiency in this respect. Among field populations in this country less efficient races prevail. For the transmission of WSV to be effected it was necessary for the vector to remain on the host for at least nine hours, but it seems that a shorter period might suffice. Extracts of crushed leaves of wheat plants suffering from the striate disease and from infective leafhoppers failed to cause infection when inoculated mechanically (by rubbing, injection) into plants. Attempts to achieve transmission through the soil or by dodder (Cuscuta campestris Yunck.) gave negative results. It was not possible to determine the thermal inactivation point of the virus in the live vector. The mosaic (zakuklivanie) virus of oat and the Russian mosaic of winter wheat as described in the U.S.S.R. differ from OSDV and WSV among other points by the production of typical inclusions and by the fact that they can easily be induced to crystallize.

The persistent nature of oat sterile-dwarf virus (OSDV) and wheat striate virus (WSV) has also been examined in an experiment using larvae of the vectorCalligypona pellucida Fabr. These larvae were grown from eggs under conditions excluding the possibility of their contamination by feeding on virus-infected plants. The eggs were from females of a population in which preliminary tests had shown that 14.4% of the individuals were non-infected, 61.2% infected with OSDV, 1.9% infected with WSV and 22.5% infected with OSDV and WSV simultaneously. Several months of individual examination of the infectivity of control larvae, which had never had the opportunity to feed on virus-infected plants, showed that none of them transmitted OSDV, although their parents were infected with it to a high degree (83.7%). On the other hand, 14.9% of the insects transmitted WSV, with which their parents were infected to a lesser degree (24.4%). Thus the larvae concerned must have acquired WSV transovarially from the female parents, and this must have taken place in a high proportion of cases. This remarkable characteristic enabled WSV to be separated from OSDV, with which it often occurs in Czechoslovakia. Larvae which went through acquisition feeding on WSV-infected oats showed, as compared with the control, a 61.6% increase of infectivity after a period corresponding to 26 to 34 days' circulation period of the virus in the vector's body and an increase of 98.2% after a circulation period lasting 40 to 51 days. Evidently mutual antagonism between OSDV and WSV in the body of the vector does not arise, since the infection of a leafhopper with one virus does not seem to prevent its infection with the other. Cross protection between OSDV and WSV in the host cereals either does not exist or is quite insignificant, because the hosts can suffer from both viruses at the same time. However, the symptoms of one virus can be masked to a varying degree by the symptoms of the other.

A description is given of the production of two types of chimera between tomato and nightshade (Solanum koelreuterianum Winkler andS. geartnerianum Winkler).
In the case ofS. gaertnerianum the micromorphological and anatomical characters showed no signs of the significant specific reciprocal effect of one tissue on the other.
The seed progeny of theS. gaertnerianum chimera resembled the control nightshade plants in all the characters investigated.
The following characters were studied: Size of stomata, shape of stomata, shape of trichomes, fruit epidermis, section through the petiole, section through the leaf blade and number of seeds.

1. It was found that fluoride has a more pronounced inhibitory effect on the respiration of wheat leaves in plants grown in a solution of gibberellic acid than on that of control plants grown in water, during the entire development of the first leaf.
2. Respiration is markedly inhibited even in old leaves of gibberellintreated plants while the respiration of equally old control plants is stimulated by fluoride by 10-100%.
3. It is assumed that the shift in the equilibrium of respiratory pathways to glycolysis, as is indicated by respiration experiments, is associated with the growth effect of gibberellic acid.

Chlorophyll formation in etiolated seedlings of wheat and maize, grown for 8 days on Knop's nutrient solution with 10μg. gibberellic acid (further GA) added per ml. was investigated and compared with control plants. Under the light of fluorescent tubes of an intensity of 3000 lux a significant decrease in the amount of chlorophyll (a+b) was observed at all time intervals from 0 to 24 hr., expressed both per dry weight and per leaf length. Experimental results indicate a decreased rate of chlorophyll formation in the presence of GA.
At the same time, a lower content of carotenoids was found in etiolated plants than in controls grown in absence of GA.
The colorimetric determination of the pigments was accompanied by paper chromatography which served as a control of quality and approximate amount of pigments.

Humus acid (Humussäure Riedel de Haen AG. Seelze Hannover) in 0.01% concentration increases the respiration intensity of plant roots grown in water cultures both as regards O₂ consumption and CO₂ production, while RQ (CO₂:O₂) is only very slightly increased. The plants used in these experiments were the winter wheat Pyšelka (Triticum vulgare Vill.), maize Zaj íček's "Český koňský zub" (Zea mays L.) and the gourd Veltrusská velkoplodá (Cucurbita maxima L.). O₂ consumption and CO₂ production were determined on separated root tips by the direct Warburg method. It was found that the effect of humus acid is not only to increase respiration intensity in the roots of the experimental plants, but also their lengths and dry weights (for all experimental plants); for maize and gourd the dry weights of overground parts were also increased, which indicates that increased respiration intensity was linked with more intensive growth of the plants.

The spraying of 26-day-old sunflower plants with a solution containing 50 μg. gibberellic acid/ml. brought about morphological changes in leaves and a statistically significant increase in the leaf shape index (length: width of leaves). The number of leaves on the stem also increased, together with a rise in the value of the ratio of dry weight of stems to dry weight of leaves.

In the course of experiments with leaf samples of pumpkin, sunflower, leafy fodder kale, sugar beet, tobacco, clover and begonia several, methods of storing material were compared with the object of determining the amount of chlorophyll (a+b) after 1 to 3 months. Chlorophyll analyses checked by paper chromatography provided evidence that the most reliable method of serial analyses is the following: Leaf discs are heated in very pure anhydrous acetone to its boiling point (with some MgCO₃ present), rapidly closed with a paraffin stopper and then kept in the dark at temperatures just above 0°C. 50 leaf samples can thus be prepared for storage within 30 minutes. The decrease in total chlorophyll (a+b) content after 28 days of storage does not exceed 5%, after 84 days of storage 10% of the initial value. Chemical conversions of chlorophyll take place here which do not appreciably affect the spectrum of the acetone extract. The method cannot be applied to plants with acid-reacting cell juice (begonia, red varieties of fodder kale and the like). Other practicable methods of storage (a different storage in acetone, storage of fresh samples at +2 to +3°C, drying at +50°C, storage at laboratory temperature) bring about more serious destruction of the pigments.

Hemp (Cannabis sativa L.) was sown at intervals from November to August. For each sowing the time of flowering was recorded for male and female plants separately. Male plants usually flowered earlier than female. When the period of daylight exceeds 14 hours, that is when the days are lengthening in April, the female plants stop flowering and continue their vegetative growth. They start flowering again when the days are shortening considerably, in August, when the daylight period is about 15 hours. The male plants flower even when the day is longer than 14 hours.
In experiments during which the plants were shaded it was found that reduction of light intensity leads to an increase in the number of female plants, particularly if shading is carried out in the early stages of the plant's development.
The occurrence of intersexual plants was observed only during the short day period (11 to 13 hours), when they composed 22-30% of the total. When the day exceeds 13 hours intersexual plants no longer develop.
The grafting of plants of varying sex did not produce any sexual change-probably due to the fact that the period of vegetative approximation was short.

This paper presents a summary of new evidence for regarding sterility and dwarfing of oats (OSDV) as a virus disease. Brief references are also made to the identification of a further virus in Czechoslovakia-the wheat striate virus (WSV). Both viruses are transmitted by the leafhopperCalligypona pellucida F. The wheat striate virus differs from the oat sterile-dwarf virus in that it can be passed transovarially by the infected females of the vector to their progeny. This characteristic, which made it possible for the two viruses to be separated from each other, was demonstrated for the first time for pathogenic viruses on the European continent in this case. OSDV can be transmitted by leafhopper larvae and adults. The time during which OSDV circulates in the vector's body is very variable; it is usually three to four weeks. The incubation period of OSDV was three to four weeks for oats, four to seven weeks for wheat and barley; rye only showed retarded growth after four weeks. For infection to take place it was necessary for the vector to remain for a minimum of half-an-hour on the test plant; 100% infection was obtained when the vector remained on the plant for three days. The injury inflicted by OSDV on the host does not increase proportionately either with the duration of the feeding period or with an increase in the number of vectors on the plant. Concentrated extracts of the crushed bodies of infectious leafhoppers produced no symptoms of disease, when rubbed or injected into oat plants. Nor were attempts to transfer OSDV and WSV through soil or dodder successful. OSDV was, however, transferred by grafting. Both viruses gave rise to characteristic symptoms inAvena fatua L. andPoa annua L. These findings are discussed from the etiological point of view.

1. Leaves of sugar-beet (Beta saccharifera), which had assimilated active carbon dioxide C¹⁴O₂, were subjected to the process of humification in soil. After three to five months of humification the dried soil was extracted with ether-alcohol, then with sodium or potassium hydroxide; the humic acids were separated from fulvic acids with hydrochloric acid. All fractions were radioactive.
2. Maize plants (Zea mays) grown in diluted Knop's solution with the addition of active humic acid showed radioactivity in the roots and leaves. There was, however, a marked difference between the roots and the leaves. While the activity of the roots after two to twelve days was about 100 to 200 cpm., that of the leaves was about 20 cpm. as calculated for one plant, or about 300 cpm./10 g. for roots and at the limits of measurement for leaves.
3. When a drop of solution and suspension of active humic acid was placed on the lower surface of the first leaf, it spread very little even in this leaf; the activity of the second and third leaves was at the limits of measurement after five days; the same applies to the roots.
4. Autoradiograms were fully in keeping with the results obtained with the counter. Roots were clearly marked and more or less intensely, while the leaves did not appear or appeared only as faint shadows.
5. These experiments do not resolve the question of whether unchanged humic acid penetrates into the cells. It can only be concluded, on the basis of these experiments, that if radioactive humic acid is added to water or to nutrient solution, radioactivity appears in the roots and later weakly in the leaves. If it is assumed that the activity measured in the plant organs was caused by humic acid applied direct, this means that it penetrates into the plant slowly, it is not accumulated and spreads throughout the plant slowly from the roots.