The effect of temperature on the number of lesions and the time of their appearance was studied by inoculating French bean leaves (Phaseolus vulgaris L. cv. Perlička) with lucerne mosaic virus either 24 or 48 h before or, 24 or 48 h after they were exposed to various temperatures. The temperatures tested were 23, 25, 27, 30, 33 and 36° C.
Before and after such exposures the plants were kept in a constant temperature of 25° C. By increasing the temperature before inoculation the number of lesions increased in comparison with the control. The optimal temperature for the maximum number of lesions is between 27° and 30° C. There is no significant difference between those experiments when the exposure time was 24 h or 48 h before inoculation. The same temperatures applied for 24 or 48 h after inoculation have a decreasing effect upon the number of lesions formed by LMV on French bean leaves. The decrease is 30 to 75%. In this case the first necrotic local lesions appeared 42 h after inoculation when exposed to higher temperatures above 27° C for 24 h, and 60 h after inoculation when exposed to these temperatures for 48 h. The shape of lesions varied a little in both cases as the pictures show.

In Wurzelhomogenaten aus Keimlingen der Modellpflanze Sinapis alba L., die durch Pyridinderivate in der Konzentration 5×10^-4 M beeinflusst worden waren, wurden Aktivitätsänderungen der Glucose-6-phosphat-Dehydrogenase gefunden: Phenäthylpyridine (IA, B, C) und trans-Styrylpyridine (IIA, B, C) steigern die Enzymaktivitätin vivo, in vitro führen sie jedoch zu einer deutlichen Hemmung. Der dritte Strukturtyp, Pyridylphenazetylene (IIIA, B, C), istin vivo zwar unwirksam, doch in denin vitro Versuchen war er noch wirksamer als die beiden vorher genannten Typen. Es ist wahrscheinlich, dass die Ursache der Enzymaktivitätssteigerung in der Steigerung der NADP-Biosynthese liegt. Die Erhöhung dieses Koenzyms kann den Kohlenhydrateabbau zu Gunsten des oxydativen Mechanismus, des Pentosecyclus, zur Folge haben.

Labelled carbon dioxide was supplied for 22 hrs to a leaf of the leader or to the lateral shoot in two-year-old apple seedlings. The distribution of radioactive assimilates within the plant following this treatment was investigated by using radioautography.
The transport of labelled assimilates from the young leaf of the leader was very meagre and affected only parts of the stem and the leaves situated in the close vicinity of the treated leaf.
The¹⁴C-labelled assimilates from the mature leaf of the leader were transported in a considerable amount to the apex and to the other leaves of the leader. They were also found in an appreciable amount in the stem and the roots, as well as in some lateral shoots.
After supplying¹⁴CO₂ to the lateral shoot remarkable transport of labelled assimilates was observed. Radioactivity was detected in the tip and in the youngest leaves of the leader, as well as in the roots. Their path in the stem was studied by dissecting the plant and examining the cross section from each internode. This method revealed that the assimilates from the treated leaf or shoot were transported downward only on one side of the stem in a helical pattern. The lateral shoots situated on the radioactive side of the stem were also labelled, whereas those situated on the opposite (non-radioactive) side were not labelled.

The callus tissue derived from tobacco pith and subcultured for 5^1/2 years on a solid synthetic modium revealed considerable differences in cell division activity depending on the age of the subculture and diurnal rhythm. The callus cells exhibited different level of ploidy among which an aneuploid condition nearer to diploid (2n=30-50) predominated. Chromosomal bridges and other structural rearrangements (lagging chromosomes, fragments) were observed in ana-and telophase.

The Euonymus Mosaic Virus was isolated fromEuonymus europaea. The virus was transmitted by sap to cucumber and other test plants, by seeds orAphis euonymi F., and it was soilborne, too. The sap from cucumbers lost its infectivity after 10 minutes at 80°C and after 35 days at 20-22°C. It is probably a new virus so far not described. The investigations of this problem are not finished, yet.

Morphactin-butylester (a flourene-9-carboxylic acid derivative) inhibited seed germination of two strains of lettuce. Morphactin induced inhibition of germination could be partially or wholly reversed by simultaneous addition of gibberellic acid. However, gibberellic acid played very little part in reversing the inhibitory effect of morphactin on seedling growth. It is concluded that gibberellin can not reverse all the growth effects induced by morphactin.

L'aire d'écoulement du latex a été déterminée sur le tronc de l'Hevea brasiliensis à l'aide de Rb⁸⁶ inoculé avant la saignée à diverses distances de l'encoche. Une telle détermination peut être effectuée par une extrapolation non linéaire des courbes de drainage ou par une formule mathématique. Dans ce dernier cas, il suffit de connaître la quantité totale de latex écoulée depuis le début jusqu'au moment de l'apparition du latex radioactif provenant d'un point d'inoculation.
Les courbes d'écoulement du latex radioactif ayant plusieures maxima, correspondant aux divers points d'inoculation de Rb⁸⁶, peuvent être utilisées pour calculer les quantités relatives de latex écoulées de ces points. Dans ce but, on doit déterminer la radioactivité du latex aux points d'inoculation du Rb⁸⁶ dans l'écorce avant la saignée et réconstruir le parcour des courbes d'écoulement du latex radioactif pour les inoculations individuelles. Les quantités de latex déterminées de cette façon, provenant de diverses distances de l'encoche, se trouvent en bon accord avec les contractions de l'écorce aux mêmes endroits.
On a déterminé à l'aide de Rb⁸⁶ la forme de la partie principale de l'aire d'écoulement et on a comparé sa longeur à celle de l'aire de déplacement, délimitée par la contraction de l'écorce et par le déficit en latex dans l'écorce. La longeur de l'aire de déplacement a été trouvée deux fois et demie plus grande que celle de l'aire d'écoulement. La quantité totale de latex écoulé correspond à 80 % de la quantité mis en mouvement dans l'écorce lors de la saignée.

The present work is a study of the frequency of polyvalents in autotetraploid kohlrabi, cabbage and their intervarietal hybrids. Polyvalents were stated in the final phases of heterotypic prophasis, usually in diakinesis.
In none of both varieties any significant relationship between frequency of polyvalents and fertility expressed by mean number of seeds per siliqua was found, while in intervarietal hybrids some correlation was observed between mentioned characters. This leads to the conclusion that the frequency of polyvalents is not always a measure of the degree of fertility in auto-polyploids.
Autotetraploid intervarietal hybrids were characterized by marked prelevance of bivalents, by a considerable percentage of well-developed pollen grains and by high correlation between frequency of polyvalents and fertility. These characters are typical rather for amphidiploids.

The time course of fertilization in barley is described and the observations compared with those of older authors. The triple fusion is terminated in spite of its late onset always before syngamy. Whereas the time period reported for the so-called preparatory phase of fertilization and for the division of the primary endospernal nucleus is similarly reported by many authors, there are difference of as much as 8 hours in various report on the beginning of the division of the zygote (beginning of the prophase 13-21 hours after fertilization). In the present material, the zygote began to divide latest.
The transient reserve substance representing an energy store for fertilization in barley was found to be starch. Barley belongs to the species in whcih starch is formed in the pollen grain and the pollen tube itself. When the content of the pollen tube is released, part of it arrives in the embryo sac. A mature embryo sac contains many starch grains near the nucleus of the oosphere and the polar nuclei. Gradual hydrolysis of this starch is related to the more rapid triple fusion and the slower syngamy.

The chlorophyll mutation rate on a large number of plants after the dose rates 0.004-16.800 R/day during the whole vegetation cycle was examined. The mutation frequency increases as early as after the dose rate 4 mR/day. The dose rate of approximately 8 mR/day is necessary to double the mutation frequency.

Dispersing of splits of NaCl and KCl during the drying process has been found using labelled²⁴Na and⁴²K preparations. This bursting effect can cause some misinterpretations in biological experiments with plant material.

The effects of low doses of two mutagens (UV-light and ethyl methansulphonate) on the growth of algae on a solid minimal (anorganic) medium were studied. It was supposed that low doses of mutagens will be more suitable for the induction of growth mutations.
The UV-light had an inhibitory effect in the whole range of the applied doses on the growth of colonies of algae from the cells inoculated on the solid medium immediately after irradiation.
Ethyl methansulphonate produced growth stimulation if applied in the lowest doses. The growth was inhibited in a further range of doses and then there appeared the range of lethal doses.
The growth responses to the influence of these mutagens were different in all the three algal species used and to the previous cultivation conditions before their exposure to the mutagens. It is certain that most of these growth responses are only modifications.
The influence of ethyl methansulphonate differed according to the method of application. If it affected the algae for a long time (it means if they were inoculated directly on the solid medium containing mutagens), or, if the algae were exposed to its influence immediately before their inoculation on the solid medium, the growth responses of colonies were quite different.
Growth responses with the single studied strains differed quantitatively only.

Irradiation with visible light reduced the mutagenic activity of 1-methyl-1-nitrosourea (MNH) and 1-methyl-3-nitro-1-nitrosoguanidine (MNG) solutions during their application onArabidopsis thaliana seeds for 24 hours. The antimutagenic effect of light was stronger with MNG than with MNH and in solutions buffered to pH 5 than in aqueous solutions. The decrease of activity of both the mutagens corresponded with the rate and degree of their photolysis. In the paper are presented the curves for the dependence of the decomposition of both substances and the formation of nitrous acid on pH and temperature of the solutions, amount of seeds.

Using paper chromatography and conventional methods of isolation, natural growth inhibitors were isolated from green leaves of different plants (Brassica oleracea, Zea mays, Pisum sativum andSalix rubra). All isolated inhibitors were found to be phenolic compounds and the chemical structure of most of them was determined; only the final structure of theBrassica inhibitor has not yet been ascertained. 500 mg of natural inhibitor ofPisum sativum was isolated from 1500 g of leaves and was identified as quercetin-glucosil-p-coumarate (QGC), described earlier byFuruya, Galston andStowe (1961). The structure of the natural inhibitor ofZea mays (4 mg from 100 g of leaves) was identical with p-coumaric acid and the chemical nature of the plant growth inhibitor fromSalix rubra (700 mg from 1,5 kg of leaves and young bark) was that of 2-chalconaringenin-glucoside or isosalipurposide, described earlier byCharaux andRabaté (1931) andHarborne (1966). All isolated substances had inhibiting properties in the straight growth test of wheat coleoptile sections and decreased the growth of isolated stem sections prepared from plants-donors of inhibitors. Thus, maximum growth inhibition (LG max) was attained, if wheat coleoptile sections were incubated with:Brassica inhibitor in the concentration of 0.5 mg/ml, withPisum inhibitor (QGC) in the concentration of 16 mg/ml, withZea inhibitor (p-coumaric acid)-0.35 mg/ml and with Salix inhibitor (isosalipurposide) in the concentration of 0.5 mg/ml. In small concentrations no mentioned substances were able to enhance the growth as actively as indolic auxins (on 250-300%); only slight growth activation in biotests was sometimes observed for low concentrations. Inhibition in p-coumaric acid was much more active in a free form than in the bound form as an acyl-rest of QGC. As a rule, the wheat coleoptile test was much more sensitive (3-5 times) to the plant growth inhibitors, than tests prepared from tissue and organs of plants-donors. The retardation activity of plant growth inhibitors is not correlated with their molecular weight. Dormin (or±abscissin II) was also tested on wheat coleoptile sections. In neither of the applied concentrations (10-0.05 μg/l range) was dormin able to depress straight growth of wheat coleoptile sections, but even in a 1.7 μg/l concentration it inhibited the IAA-activated growth of sections. However, additional experiments showed that dormin in higher concentrations (40 μg/l and more was able even to depress endogenous straight growth of wheat coleoptise sections. The differences between the properties of natural phenolic growth inhibitors and dormin were discussed.

In estimating the water-holding power and thus also their drought resistance, the portion of curvature as shown by the desiccation curves (transpiration, loss curves) appears most suitable in which the water-binding forces within a plant body feature a steep and characteristic rise. Since this portion of the curving stage coincides, in the majority of cases, also with the linear stage for the desiccation curves as described byCetl, this author's method of establishing drought resistance of plants (Cetl, 1953, 1957) may be applied to good advantage also to the woody species seedlings. For particularly urgent instances serving the purpose of orientation a modification of this method has been suggested, as follows: following cutting off the seedling the output of water is weighed at these intervals only: 0, 60, 120, and 240 minutes; as the criterion for drought sistance the resulting value for the rate of water output (v) is taken as measured between the interval of 60 and 120 minutes. When a detailed analysis is made it is advisable to consider the v value measured for the interval between 0 and 60 minutes and for that between 120 and 240 minutes. Moreover, it is likewise advisable to maintain the soil with experimental seedlings at the level of optimum moisture (60 to 80 per cent maximum capillary water capacity), for some 18 to 22 hours prior to the seedling's abscission.

The effect of 2-thiouracil on vegetative growth and floral differentiation was investigated inChenopodium rubrum plants grown in water cultures. Between the low concentrations of the agent, stimulating vegetative growth and floral differentiation, and those inhibiting both these processes, a narrow concentration range was found (1.10^-5 m to 2.10^-5 m), where growth was inhibited selectively. At a concentration of 1.10^-4 m a selective inhibition of development was found when 2-thiouracil was applied at the beginning of photoperiodic induction. Inhibition of development was strong regardless of whether 2-thiouracil was applied before, during or closely after 4 days of photoperiodic induction; the degree of growth inhibition, however, changed in dependence on photoperiodic induction. The strongest relative inhibition of development, calculated as a ratio between development and growth, was observed always at the beginning of photoperiodic induction.
Investigation of plant growth as well as the anatomical and autoradiographic study after the application of 2-thiouracil indicate that the inhibition becomes evident at the end of 4 days of application by an overall growth inhibition and a decrease of mitotic activity. Reversal by uracil was possible after simultaneous application of 2-thiouracil. The nature of the selective inhibition is discussed and two possible interpretations of the data obtained are analyzed: a) different response of growth processes in apices and young vegetative organs respectively with regard to different participation of cell division and elongation, b) specific inhibition of floral differentiation.

In young pumpkin plants, the phosphorus was found not to be affected substantially by potassium deficiency whereas the deficiency of calcium has marked effects. Potassium distribution is not affected substantially by either phosphorus or calcium deficiency.
In short-term experiments, the presence of calcium affects markedly the total uptake of potassium but the potassium distribution remains unaltered. The stimulation of potassium uptake is far more pronounced in plants pre-cultivated in a complete nutrient solution than in those pre-cultivated in a calcium-deficient one; this is apparently due to profound metabolic changes taking place in plants grown without calcium.
The reserves of phosphorus and potassium stored in the cotyledons are easily mobilized and translocated so that they can be used for growth in early stages of development; the appearance of pathological symptoms of phosphorus or potassium deficiency is thus prevented.

Using moving boundary electrophoresis in a veronal buffer, pH 8.5, of 0.05 ionic strength and at 4.3 mA, we succeeded in separating the inhibitor, which was obtained by fractionation on a Sephadex G-50 column, into four components. The two most substantial components represent 25% and 65% respectively from the separated proteins as a whole. The heterogeneity of the inhibitor was proved by analytical ultracentrifugation, too. The ionex chromatography was applied for the quantitative separation of the inhibitor. We used ionex chromatography on DEAE Cellulose the concentration gradient being 0-1m NaCl in a 0.01m phosphate buffer, pH 7.3, and on DEAE Sephadex A-50 using the same concentration gradient in a phosphate buffer, of 0.1 ionic strength and pH 7.3. In both cases four components were obtained. The most substantial component, representing 65% of the whole analysed material, was eluted at the concentration 0.15-0.3m NaCl, and was electrophoretically homogenous and showed the most effective inhibitory ability.

The lignine content and mechanical rigidity of siliquae ofBrassica napus L. ssp.oleifera f.biennis, cv. Třebíčská were studied. Experimental plants were harvested in five consecutive periods and developmental stages of siliquae were determined on the basis of the weight of 1000 seeds. During the development of siliquae a gradual accumulation of lignine takes place; the content reached its maximum in certain developmental phases and then decreased. The mechanical rigidity of siliquae had a similar tendency. There were statistically significant differences in both properties studied within individual developmental phases. A highly significant positive correlation was found between lignine content and mechanical consistency.

The induced meiotic abnormalities as a result of sprayingVicia faba plants with aqueous saturated solutions of podophyllin and 8-hydroxyquinoline were studied. The 2 drugs induced the same types of abnormalities including lagging chromosomes, stickiness, and bridges. The main difference between the 2 agents was the induction of polyploid P.M.Cs. by 8-hydroxyquinoline.

Development of the shoot apex up to floral differentiation was investigated in the short-day plantChenopodium rubrum. The changes occurring in the apex from energence until full opening of the cotyledons (Figs 1-4), development during photoperiodic induction (Figs. 5-8), as well as the resulting floral differentiation (Figs. 9-10) are described. It was aimed at excluding the influence of plastochron changes on the interpretation of ontogeny of the shoot apex. For that reason two planes of longitudinal sections and two plastochron stages were compared.
In young plants zonation does not become fully evident prior to floral differentiation. The anatomical structure of the shoot apex does not change substantially during the first two inductive cycles which proved to be obligatory under the given experimental conditions. The changes occurring during two further inductive cycles correspond to the total activation of the meristems as manifested by the growth and branching of the apex preceeding floral differentiation proper.

The presence of potassium humate (commercial sample of Humussäure Riedel-de Haën A. G., Seelze-Hannover) in distilled water led to an increase in the content of alanine, aspartic and glutamic acid in the overground parts of wheat plants as compared with the content of these substances in control plants grown in distilled water. In plants cultivated on nutrient solutions a higher level of alanine and glutamic acid and a considerably lower level of amides was found than in plants grown in distilled water and in water with humate. Generally the content of amino acids was higher in the overground parts than in the roots after a cultivation period of one week as well as of 14 day. In the overground parts of 1 days old plants the level of aspartic acid, asparagine and alanine was found to be higher and that of glutamine lower than in seven days old plants. In the roots of the examined plants a decrease of the amino acid content accurred almost in all cases after a cultivation period of 14 days as compared to one of 7 days.

In der meristematischen Zone, Streckungszone und in der Zone der beendeten Zellstreckung der Wurzeln vonVicia faba L. cv. Chlumecká, wurde festgestellt, dass 8×10^-2 m NaF und 10^-3 m Monojodessigsäure den Q_{O 2} in der Streckungszone und der Zone mit beendeten Zellstreckung am meisten und in der meristematischen Zone am wenigsten hemmen. Bei der Applikation des Malonats in der Konzentration 5×10^-2 m sind die Unterschiede zwischen den einzelnen Zonen statistisch nicht gesichert, der RQ wird jedoch erhöht, besonders im Meristem. Von den angewendeten DNP Konzentrationen wirkt die Konzentration 10^-5 m auf den Q_{O 2} und Q_{CO 2} stimulierend; bei dieser findet die höchste aerobe Gärung im Meristem statt. Bei höheren DNP Konzentrationen wird der Q_{O 2} im Meristem gehemmt, es kommt die höchste Q_{CO 2} Produktion und auch die höchste aerobe Gärung in der Streckungszone vor. Durch 10^-2 m 1-Amino-2-naphtol-4-sulphonsäure werden Q_{O 2}und besonders Q_{CO 2} in der Streckungszone und der RQ im Meristem beschleunigt.
Diese Ergebnisse zeugen für den höchsten Anteil der Glykolyse in der Streckungszone; dies stimmt jedoch mit den Versuchen mit dem Verbrauch spezifisch markierter 1-¹⁴C und 6-¹⁴C-Glukose, den gefundenen RQ und dem Vorkommen des Äthanols nicht überein. Diese Diskrepanz zwischen den Ergebnissen verschiedener Methoden wird weiter verfolgt.

The cryosestonic unicellular green algaKoliella tatrae (Kol) Hind., which grows in the surface layers of the summer snow-fields of the Vel'ký Žl'ab valley in the Belánske Tatry Mountains (Czechoslovakia), was started to be cultured at the laboratory. This alga may be considered as a typical (true) cryobiont, the optimal growth of which requires about 4°C; long-lasting temperatures ranging from more than 10°C have a lethal effect. The low-temperature strain obtained is suitable for the comparison with unicellular green algae, used as models for the study of the photosynthetic activity and metabolic processes of autotrophic micro-organisms (Chlorella, Scenedesmus, etc.).

A study was made of the effect of different constant soil moisture (90, 60 and 30 or 40% maximum capillary capacity) on the net assimilation rate (N.A.R.) in maize in relation to changes in relative transpiration (R.T.), water saturation deficit of the leaves (W.S.D.) and osmotic pressure of the cell sap (O.P.). The soil moisture was maintained constant either from the planting of the germinating grain, or from the phase of 4-6 leaves. An attempt was made to interpret the mechanism of action of water deficit on photosynthesis and at a rough differentiation between the indirect effect through changes in internal diffusive resistance to carbon dioxide and the direct effect on the hydration of the photosynthetizing tissue. In plants exposed to different constant soil moisture levels from the phase of 4-6 leaves, the initial difference in N.A.R. corresponding to the degree of lowering of soil moisture gradually evened out during the vegetation season. On applying different constant soil moisture levels from the time of planting no marked differences in N.A.R. were found between plants cultivated at high values of soil moisture (60% and 90%). In plants cultivated from planting at 40% soil moisture, the course of changes in N.A.R. was qualitatively different from that of the above two variants and corresponded more or less to changes characteristic for the process of adaptation to unfavourable conditions. From the analogous course of N.A.R. and R.T. it can be assumed that in all cases the intensity of photosynthesis was very markedly influenced by changes in diffusive resistance to carbon dioxide. On the basis of an analysis of changes in O.P. of the cell sap and W.S.D. of the leaf tissue, the assumption was made that in plants cultivated from planting at 40% and to some extent at 60% soil moisture, irreversible adaptation changes occurred in the structural conditions of photosynthesis as a result of continuous dehydration. In plants cultivated at similar soil moisture levels from the phase of 4-6 leaves, the changes in the intensity of photosynthesis were more likely caused by actual dehydration of the photosynthetizing tissue.

This work is a continuation of a communication on the stainability of broad bean (Vicia faba L.) root tip cells with alcian blue, published some time ago. Following the standard method of staining with alcian blue, the cell walls are very strongly stained, the nuclei (except nucleolus) lightly, the nucleolus and cytoplasm are practically colourless. The weak dyeing of the nucleus is not equal throughout the whole section so that the comparison of stainability of cell walls and nuclei by itself cannot explain the staining with alcian blue. The results of this work on the staining of cell walls (if not including model experiments and experiments in vitro, which are not considered as decisive here) can be summarized as follows: the pH dependence of staining, the loss of stainability as a result of pectinase digestion, blocking of staining by methylation and regeneration of stainability by demethylation and, finally, the impossibility of staining in the presence of NaCl lead to the conclusion that the staining of the material studied in this work is primarily caused by the salt linkage of alcian blue with the free carboxyls of pectic substances. From the comparison of staining with alcian blue and with other basic dyes it follows that in the case of alcian blue some other factors may also take part and are the reason for the selectivity and firmness (fastness) of the staining of cell walls with this dye. Otherwise, the staining of plant cell walls with alcian blue corresponds quite well to the staining of carboxyls containing polysaccharides of animal tissues with this dye. By staining with alcian blue it was found impossible to distinguish between younger and older cell walls within the meristem. However, this staining is suitable for routine use when studying the meristematic tissue. It is often possible to use solutions of a higher pH than generally used.

Experiments were conducted to compare the efficiency of transmission of a strain of pea mosaic virus (PMV) isolated in Czechoslovakia by two strains (clones) of the pea aphidAcyrthosiphon pisum Harris (green and red) and one strain ofMyzus persicae Sulz. PMV is a nonpersistent virus and the preliminary fasting of aphids before acquisition feeding increases the efficiency of aphids in transmission of this virus. In our experiments two hour fasted individuals were used and two periods of acquisition feeding on the source (1 and 5 minutes). On the healthy test plants the aphids were left over night. As the source and test plants pea (Pisum sativum L.) of the cv. Raman were used. During the one minute acquisition period on the source of infection the aphids were observed under the stereoscopic microscope. They usually made two to three probes. During the five minute acquisition feeding time the aphids were not observed and they were taken from the source of infection after a lapse of five minutes. To compare the efficiency in transmission of this virus by these aphids only one aphid per tested plant was used and in all trials only two to four day old nymphs were taken. Differences in transmission efficiency between two strains ofAcyrthosiphon pisum Harris were highly significant. The green strain of pea aphid was the less efficient vector in comparison with the green peach aphid and the red strain of the pea aphid, the latter being the most efficient vector of this virus.

The biological effect of barley root excretions was studied during a 4 to 10 days cultivation period. The effect of root excretions changes according to the cultivation period of barley. It was ascertained by means of a bioassay that growth was either conclusively stimulated or the root excretions did not affect growth of the roots and of the upper part ofNasturtium. No significant inhibitory effect was observed. The effect of the single amino acids and of their mixtures found in the root excretions of barley was quite different. The following amino acids were determined by paper chromatography in root excretions: alanine, asparagine, phenylalanine, glycine, leucine, lysine, serine, tyrosine, glutamic acid and valine plus methionine. During cultivation their total quantity increased from 5.48. 10^-5 up to 1.13. 10^-3 mg per plant. Most of the 20 amino acids observed, displayed in theNasturtium test at a concentration from 0.1 to 1,000 mg/l an inhibitory effect onNasturtium growth. The effect of amino acid mixtures, corresponding qualitatively and quantitatively to the free amino acids in barley root excretions was dependent on their concentration.
Growth regulators of the auxin type were found in culture solutions by chromatographic separation and with bioassay. As it may be seen from the results obtained, there are besides amino acids and indole derivatives other non-identified compounds involved in the effect of barley root excretions.