The work presented in this paper was a study of the influence of different isolated humus substances when applied to the overground parts of plants by spraying on the leaves. The humus components employed showed varying effects on growth, respiration and chlorophyll content inBegonia semperflorens Link et Otto. The result of the physiological changes is reflected in morphological changes of the overground parts and particularly in the structure of the root system. Fulvic acids were found to be the most effective of the humus components when sprayed on leaves.

The seeds contain such a high percentage of phosphoric acid that it interferes with the obtaining of correct results in analysis. Its prior removal from the solution of ash is therefore necessary. A new method is suggested for the entire analysis which is a combination of percolation through an ionexchanger column and colorimetric and gravimetric determination.
The oxide values and the average content of ash per 100 g. dry weight of seeds ascertained by analysis were used to calculate the weight of each determined element per 100 g. of dried substance.
The analysis showed that traces of tin are present in the ash of the seeds tested.
Under the given conditions each species maintains its characteristic way of storing ash constituents in the seeds and this is not obviously affected by the affinity of the plants or the influence of the soil.

Root formation was studied in cuttings from tomato plants infected with stolbur and Czechoslovak type II potato witches' broom viruses. A highly significant difference in root formation was always found in plants with clear-cut disease symptoms. Potato witches' broom virus inhibited the root growth more than stolbur. In all cases, diseased plants showed a greater variability in the weights of roots than healthy controls.

The barley variety "Browarny P.Z.H.R." was grown in pots. Experiments on the course of development were conducted for two years. The increase in the dry weight of roots, leaves, stems and grain was recorded. The assimilation area of the plants was measured periodically and the rate of respiration in detached leaves was determined. Photographic records were kept of growing point and ear development. The dynamics of growth and development were studied during the whole vegetation period. The present results are similar to those previously obtained for spring wheat. The short period of leaf activity is the chief factor limiting barley growth.

Statmographs were used for determining the curves of weight decrement of severed root tips of the squash (Cucurbita maxima L.) with time and were examined under controlled conditions. The existence of two qualitatively different fractions of water could not be demonstrated by the method used, all the curves obtained displaying a completely continuous character, without any inflexion point. The basic shape of the curves remained preserved on desiccation at different temperatures (20-40° C), at different relative humidity (45-90%), with plants of different age and different composition of aqueous media (Knop's nutrient solution, calcium-free medium, distilled water). Not even a 0.01% solution of potassium humate which significantly raised the water content of root tissue affected the shape of the desiccation curves. A continuous release of water was also observed when the meristematic root zone and the zone of longitudinal growth were dried separately.

One of the criteria employed for evaluating the resistance of plants to drought is their ability to endure the effects of water deficit with no irreversible changes in their tissues. This ability was investigated by means of a method described in this paper. The leaves of some xerophilous grasses (species of the genusStipa, Melica, etc.) were left to dry up under precisely defined experimental conditions so that they reached various degrees of water saturation deficit. Then they were cut up into segments and-mounted in a special frame-were saturated with water. The initial deficit and its compensation were investigated gravimetrically. The resultant values were plotted on a graph. Whereas in some instances the water loss from the leaves during desiccation was linear, the compensation curve exhibited a characteristic breaking point which indicated the degree to which the water loss could be compensated, and when the changes became irreversible. It was found that the studied series of plants of typical continental species have the capacity to supplement their water content ad integrum even in the case of considerable water deficit. Plants living in regions of a more oceanic type do not exhibit this property. It is probable that this property will also be of much value in the explanation of causal phytogeography.

Chromatographic analysis of wheat leaves grown for 4 to 10 days in a solution of gibberellic acid (10-20 p.p.m.) revealed a higher level of fructose-1,6-diphosphate as compared with that of 3-phosphoglyceric acid and phosphoenolpyruvic acid, and of 3-phosphoglyceric acid as compared with that of a hitherto unidentified phosphate. These changes were found under different light regimes which preceded extraction of phosphates from leaves. On the basis of these data and in view of earlier results (Luštinec, Pokorná, Růžička 1962) it is assumed that glycolysis interacts with reactions utilizing its intermediate products for the synthesis of lipids, this representing a possibility of bringing about changes in leaf phosphate levels due to gibberellic acid. In order to verify the postulate the incorporation of 1-¹⁴C- and 6-¹⁴C-glucose into lipids, phospholipids (the magnesium salts of which are insoluble in acetone), carbon dioxide and the non-lipid fraction of leaves was investigated. It appeared that the incorporation of 1-¹⁴C into the lipid fractions of plants grown for 3-7 days in a gibberellic acid solution is markedly lower than that of 6-¹⁴C. The ratio of radioactivities C₆∶C₁ was increased in the lipids by the three-hour treatment of leaves with gibberellic acid (10 and 50 p.p.m.) during their incubation with glucose-¹⁴C. In view of the fact that the amount of substances extractable with ether is the same in the experimental and in the control leaves and that the incorporation of 1-C into lipids is frequently considerably higher in the controls than the incorporation of 6-C the effect of gibberellic acid on the rate of exchange of carbon atoms between the lipids and the products of glucose catabolism should be borne in mind.

Sodium fluoride, iodoacetate and malonate inhibit or stimulate the respiration of wheat roots cultivated for 2-10 days in a solution of sodium humate (100 mg/l.) as compared with the respiration of roots cultivated in water. The influence of sodium fluoride on the respiration of leaves is similar. The ratio of the radioactivities of C¹⁴O₂ from glucose, labelled in the position 1 or 6 (C₆/C₁) is distinctly higher in roots, but not in leaves. The change in this ratio is accompanied by a decrease in the total radioactive C¹⁴O₂ from roots of plants influenced by humate, from glucose labelled specifically and totally.
Endogenous respiration (QO₂) of roots increased in humate by 5-30%, the intensity of leaf respiration remaining at the same level. The longitudinal root growth increased in humate by 20-80%, the growth of leaves by 5-15%. The above statements show that in a humate solution the glycolytic fraction of the respiratory metabolism of roots is increased.

1. A method of "measuring strips" for the investigation of the sap exudation of crops under field conditions is described. The quantity of liquid exuded from the detopped stem stump is determined from the length of a wetted zone of a narrow strip of filter paper protected against evaporation of the liquid by a polyethylene cover bag. The strips with the cover bags can be used even to collect greater amounts of exudated liquid.
2. Using this method, the sap exudation of detopped maize plants was observed during the whole growing season. On typical curves illustrating the course of the wetting of the measuring strips, the temporary absorption of the sap from the cells and conducting elements severed by the cut, the lag in exudation and the actual sap exudation can be distinguished.
3. The length of the lag period indicates the magnitude of the momentary water deficit of the investigated plant and the rate of sap exudation indicates the availability of soil moisture.
4. The rate of sap exudation reached its maximum at the end of June and then decreased gradually. In this period also the distinct lag periods were first observed. The occurence of shorter lag periods between the 5th and 29th July, i.e. in the shooting stage which from the standpoint of precipitation is critical for the height of yield, signifies that the critical stage probably coincides with the period in which the natural disproportion between available soil moisture and transpiration may become important.
5. During the period of long lags towards the end of the growing season, the measuring strips were fastened upon the plant stumps 24 hours after the decapitation. The "exudation after 24 hours" determined in this way indicates a significant decrease at the end of August when the soil moisture dropped to a value approaching the permanent wilting percentage.
6. The results have shown that the method of "measuring strips" permits an easy and sensitive evaluation of the water relations of maize plants growing under field conditions.

When small branches of different plants were dipped after cutting into a solution of humic acid, a brown substance penetrated into vessels and coagulated there. The vascular bundles were stained to the height of 1-6 cm after a week. The presence of the humic acid in the parenchymal cells could not be demonstrated directly, but cells with a yellow or brown cell wall remained alive (they could be plasmolysed).
Humic acid, labelled with C¹⁴ was distributed in the same way in sterile and in non-sterile plant cultures, mainly through vascular bundles.

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.