The formation of the isothiocyanate group of the aglycone of glucobrassicin (Glubr) an indole glucosinolate present in relatively large quantities in plants of the familyBrassicaceae, was studied. Labelled Glubr was synthesized from L-tryptophan-3-¹⁴C-amino¹⁵N in winter rape hypocotyl segments. After extraction it was finally isolated in a crystalline state by mixed crystallization with added inactive Glubr tetramethylammonium salt. The specific activity of¹⁴C and the atoms % excess¹⁵N were determined in both the precursor and the product. The ratio¹⁴C/¹⁵N as well as the values of dilution of¹⁴C and¹⁵N were in agreement in the precursor and in the final product. This shows,inter alie, that during the biosynthesis of Glubr, L-tryptophan is not deaminated. Thus the presumed isothiocyanate group of Glubr is synthesized on the α-carbon of the L-tryptophan alanine chain, the α-carbon together with the attached nitrogen pass directly from the precursor into the Glubr aglycone. This represents a type of glucosinolate aglycone biosynthesis where the carbon chain of the initial amino acid is not elongated. This finding is supported by the fact that L-tryptophan-l-¹⁴C does not yield labelled Glubr the C₁ carbon being decarboxylated during Glubr synthesis.

The meioses of four sterile species in the genusAllium which develop bulblets in the inflorescences instead of seeds were compared, namelyAllium sativum, A. cepa var.viviparum, A. carinatum, andA. oleraceum. The most important of them,A. sativum, is an ancient cultivated plant and its vegetative reproduction prevents it from more rapid evolution such as is known in generatively propagated cultivated plants.A. sativum shows fully normal meiosis. After the disintegration of the tetrads, however, the blockade of 1. pm takes place. The cause of the blockade has not yet been cleared up. Removing of bulblets appeared as having no influence on the development of microgones. It is assumed that there may be a viral phenomenon causing a disease of the tapetum without disturbing other functions. InA. cepa var.viviparum there was observed a heavy aberration disturbance in the meiosis, which had already been signalled by the mitosis. On this ground 1. pm does not occur and sterility is fully justified. The aberration disturbance does not seem to spoil the vegetative development but on the contrary to give it a vigorous character.A. carinatum andA. oleraceum are triploid and tetraploid forms; in the meiosis they form various configurations-univalents, bivalents, trivalents, and quadrivalents. The following irregular chromosome distribution results in the coming into existence of variously valuable gametes. 1. pm takes place. There is a theoretical possibility of generative reproduction (after the extirpation of bulblets).

The photosynthetic production of dry matter of discs cut out from leaves of cucumber plants severely infected withCorynespora melonis was significantly lower than that of discs from healthy plants. The decrease was found in discs from leaves both infected and symptomless. Expected inhibition agent has not been isolated up to now.

The interaction of GA and IAA in apical dominance was investigated in an experiment in which first of all an IAA paste was applied to the cut areas formed by the decapitation of epicotyl apices of pea seedlings, followed after one week by the application of a 0.25 % GA paste. The latter treatment was able to overcome the growth inhibition of cotylary buds induced by a 0.03 % IAA paste, but not that caused by 0.06 and 0.12 % IAA pastes.
The correlative function of a root in the renewal of the apical dominance can, to some extent, be directly simulated by exogenous gibberellin, as has been demonstrated in the experiment with decapitated pea seedlings deprived of one cotyledon, on which the growing axillary of the amputated cotyledon was decapitated. In this case the axillary of the remaining cotyledon grows in the plants where the root has been left, but in those deprived of the root, there appears a serial of the amputated cotyledon (Dostál, Biol. Plant. 9 : 330, 1967). When GA was supplied to the plants treated in this way, the coty lary of the remaining cotyledon grew even in the plants deprived of the root.

The first information concerning the cytogenetic efficiency of thermal neutrons in lentil are presented in this paper. The range of cytologically effective dosages of thermal neutrons in lentil was determined. This determination enables us to compare the efficiency with the mutagenic effect of thermal neutrons and with their effect on the growth and development of plants of M₁ generation. These effects were already evaluated in previous communications.
Thermal neutron irradiation significantly affected all the characters studied. A linear dependence of the effect on the dose of the neutron radiation was found for most of the analyzed characters. From a sample of scored cells, whose nuclei were in the anaphase or early telophase, 9.0 to 72.0% of them had chromosomal bridges and fragments after irradiation with dosages from 3.3×10¹¹ n cm^-2 to 4.5×10¹² n cm^-2. The highest number of rearrangements per one cell reached 2.16 after irradiation with 4.25×10¹² n cm^-2 while the lowest dosage used, 3.3×10¹¹ n cm^-2, induced 0.17 of chromosomal rearrangements per one cell. Irradiation with thermal neutrons is capable of inducing a large number of very complicated chromosome rearragements.

Structural proteins of both chlorophyll - deficient mutants, extracted with a phosphate buffer solution pH 8,3, using Triton X-100 as detergent, exhibit, in comparison with normal plants, a faint cathodic fraction giving positive staining for lipoproteins and containing chlorophyll. No differences in soluble proteins were found between the mutants and control plants. The pattern of the individual protein fractions differs according to the method employed.

The nucleic acid fractions in cotyledons of young Chenopodium rubrum plants exposed to continuous light, continuous darkness and short (8 h) day, respectively and labelled with³²P 24 h prior to harvesting were studied by means of chromatography on MAK columns. Some parameters of cotyledon growth (dry weight, cotyledon area, occurrence of mitoses) were also investigated.
The changes in the nucleic acid fractions agreed with the dynamics of cotyledon growth. In continuous light the content of all fractions increased. The radioactivity of DNA and s-RNA did not undergo any great changes and only r-RNA increased. The specific activity of r-RNA increased slightly, that of soluble RNA and DNA was reduced. In continuous darkness the content of all the fractions did not undergo any great changes. The radioactivity as well as the specific activity of all fractions decreased. In short day the content of the nucleic acid fractions did not change conspicuously. Only the specific activity of s-RNA increased in a noticeable way while the radioactivity of r-RNA and the specific activity of DNA decreased and this of r-RNA did not change. The changes in nucleic acid metabolism were partially connected with changes in³²P uptake which depended upon light conditions but they were not merely a consequence of this fact. Obviously, there also exists a more direct relationship between nucleic acid synthesis and growth.

6-azauracil (AU) and 2-thiouracil (TU) were applied to the short-day plants Pharbitis Nil and Chenopodium rubrum and to the long-day plants Hyoscyamus niger, Lolium temulentum and Triticum aestivum cv. Chlumecká 12 at different times before, during or at the end of floral induction. In wheat the effect of 5-bromouracil, 5-iodouracil and 2-thio-6-azauracil was also tested.With the exception of bromouracil, which slightly stimulated flowering in wheat, all analogues either strongly inhibited or completely blocked flowering when applied in appropriate concentrations a short time prior to induction or at its beginning. Treatments given a longer time before induction or after its termination was less effective. Inhibition of flowering was always associated with damage to the vegetative growth. The effect of TU was reversed by uracil and that of AU by uridine, if these compounds were applied simultaneously with the analogue at a concentration exceeding at least 5 times that of the analogue. Reversal also applied to vegetative growth. Simultaneous application of gibberellin and analogues did not remove the inhibition.

By comparing maize plants cultivated in standing nutrient solution with those from solutions flowing at different flow rates it has been established that absorption of nitrogen, potassium and especially of phosphorus was increased owing to the flow. There was likewise a relative rise in the distribution of nutrients to the overground parts of the plants. The content expressed per unit dry matter was increased only in the case of phosphorus; with nitrogen and potassium it was slightly lower than in the standing solution. Increasing amounts of iron were required under the conditions of flowing nutrient solutions to prevent chlorosis of the plants. The production of dry matter,NAR andRGR was also increased because of the flow. The flow considerably changed the habitus of the primary roots of the maize plants. The roots were longer, thinner and on the whole they contained relatively less dry matter (RWR). The lengthening of the roots is explained as a response to stimulation by the solution flow-the rheotropism.

Virus particles (approximately 73 nm in diam.) usually showing an inner capside (45 nm in diam.) and similar to diplornaviruses, esp. reoviruses, were found in some cells of enations inAvena sativa andArrhenatherum elatius leaves infected with the oat sterile dwarf disease (OSDD). (The same virus particles were described by the authors in 1966 in the leafhopper vector.)
Mycoplasma-like microorganisms found in1969 in the OSDD leafhopper vector were absent in OSDD infected plants. Tetracycline did not affect symptom development in plants and did not alter the infectivity of the vector.
Therefore, OSDD is apparently of virus origin; mycoplasmas-like bodies found formerly in the OSDD vector are probably not involved in OSDD etiology.

The enzymatic transamination reactions between aspartic and α-ketoglutaric acid and between aspartic and pyruvic acid were studied in fresh dialysed extracts of young wheat plants cultivated under various trophical conditions, in mineral solution (Knop), in the solution of an soil organic substance (potassium humate) and without nutrients (H₂O). Simultaneously, the level of endogenic aspartic acid, glutamic acid and the growth values were determined. The enzymatic reactions were characterized by determining the optimum pH, the time course, and the effect of coenzyme and of inhibitors.
The activity of the aspartate-glutamate transaminase from the root system of plants was considerably higher than the activity of the overground organs. The enzymatic activity from both parts of the plant was inversely proportional to the growth rate: intensive growth of the plants from the Knop variant was connected with their low enzymatic activity; the level of endogenic glutamic acid was high. The slow growth of the plants without nutrients was connected with a higher enzymatic activity; the level of endogenic glutamic acid was low. The plants from the potassium humate variant had an intermediate position between these two variants from the point of view of growth as well as from that of enzymatic activity. The plants with insufficient nutrition (slow growth, low level of endogenic glutamic acid) apparently have a low capacity for supplementing the glutamic acid deficit, which is essential for the metabolic processes, by increasing the activity of the reactions leading to glutamic acid synthesis (Asp-Glu) and, on the other hand, by decreasing the reactions utilizing it (Glu-Ala). For wheat plants the active aspartate-glutamate reaction is obviously physiologically more important than the direct reaction glutamate-aspartate and the reaction aspartate-alanine which in all cases had a very low activity.

The employment of the classic stand density experiments in studies of the horizontal organization of plant stands is very laborious and requires a large experimental field area. The procedure based on the regular thickening of plant stands is more convenient for plants grown in a lower density. A simplified modification of this method is described which keeps a constant square nutritional area regardless of the plant densities.

Papaver somniferum plants grown in pots in the phase of forming the first pair of leaves were treated by 6-4 ml of 0-02% solution of 3-amino-l,2,4-triazol (amitrol) per single pot, which is equal to the dose of 2 mg of amitrol per 100 cm² soil area One, four, seven and ten days after the application the effect of the herbicide on some physiological processes in the overground organs of plants was investigated.
Amitrol decreased the activity of catalase by 60% compared with control plants 1 day after the application, even though no external symptoms of damage were evident. On further action, the activity of catalase was suppressed somewhat less. The respiration was not inhibited by amitrol to such an extent as the activity of catalase. One day after the application the respiration was not suppressed significantly, at further dates the respiration activity decreased. The difference between the respiration of treated and control poppy plants was particularly evident when the oxygen consumption was referred to a single plant. Under these experimental conditions we failed to determine the activity of ascorbinoxidase and peroxidase. The activity of polyphenoloxidase was stimulated by amitrol from the fourth day after the treatment.
On the basis of these experiments we can say that poppy has not a physiologically based resistance to amitrol.

The effect of nutrient solutions with certain essential elements lacking, on oxidation reduction potential (RP) of the first leaf was examined in two cultivars of barley seedlings NO₃^- and K⁺ decreasedRP considerably, PO₄^3- did not. The effect of NO₃^- and K⁺ was dependent. on the illuminance. Under glasshouse conditions, the increased level of NO₃^- and K⁺ did not cause any change ofRP. In field conditions, the increased supply of nitrogen fertilizers resulted in a lowerRP in leaves at ear emergence and a higher yield. The use ofRP measurement in leaves for the estimation of the effect of mineral nutrition on plants is discussed.

The metabolism of¹⁴C-anthranilic acid (¹⁴C-AA) in kohlrabi (Brassica oleracea L. var.gongylodes L.) and the effect of radiation gamma⁶⁰Co on this metabolism was investigated. In hypocotylar segmnents of seven days old etiolated seedlings¹⁴C-AA was metabolised par, tially to its detoxication product¹⁴C-β-glucoside of AA. Simultaneously L-tryptophan was also formed, which in these plants is a precursor of indolic glucosinolates glucobrassicin and neoglucobrassicin.
The metabolism of¹⁴C-AA was followed for 97 h. Radiation, applied both to seeds and to seven days old plants did not affect the metabolism of¹⁴C-AA substantially. The intermediary reaction AA → L-tryptophan in the biosynthesis of L-tryptophan is not a radiosensitive part of the synthesis of this amino acid. A not too high radiation sensitivity (max. 45%) was observed in the metabolic pathway leading from L-tryptophan to glucobrassicin.

Metabolites of indolepyruvic acid and indolelactic acid were investigated using 2 systems: a bacterial (pea stem homogenates containing the epiphytic bacteria) and a plant system (pea stem sections under sterile conditions). The products of spontaneous indolepyruvic acid decomposition in aqueous solution and during chromatography were investigated, too.
Biological indolepyruvic acid conversion yields, besides those substance amounts which occur spontaneously, indoleacetic acid, indoleethanol (tryptophol) and (only in the sterile plant system) indoleacetaldehyde. An inhibitor extract from pea stems decreases the indoleacetic acid and increases the indoleethanol and indoleacetaldehyde gain.
Indolelactic acid is not metabolized in the sterile plant sections. Indolelactic acid oxidation by the bacteria-containing homogenate yields indolepyruvic acid and is inhibited by the inhibitor extract.

Tryptophan, tryptamine, or indolepyruvic acid were applied to 2 systems: a bacterial (pea stem sections containing the epiphytic bacteria) and a plant system (pea stem sections under sterile conditions).
In the plant system, the production of indoleacetic acid and indoleethanol (tryptophol) from each applied indole derivative is clearly reduced by the aldehyde reagents bisulfite and dimedon, respectively. Indoleacetaldehyde is chromatographically detected after alkaline liberation from its bisulfite addition product.
In the bacterial system, the production of indoleacetic acid and indoleethanol is likewise reduced by bisulfite and dimedon. However, after tryptophan or tryptamine application, we could not detect indoleacetaldehyde in the described way.
In one case only, namely tryptamine application to the bacterial system, indoleethanol production (contrary to indoleacetic acid production) is scarcely reduced by the aldehyde reagents. This indicates a bacterial pathway tryptamine → indoleethanol which bypasses indoleacetaldehyde.

1. The transfer of immature embryos from maternal plants to artificial media influenced the radial arrangement of vascular bundles in developing root primordia. The variability in the number of poles of the prospective protoxylem and protophloem, observed as a rule during embryogenesis under natural conditions, could not be suppressed even under the conditions ofin vitro cultivation. The possibility is admitted that when using agar medium the nutrient supply need not necessarily be equivalent for all embryos.
2. Using excised embryos of various ages the period of delimination of the vascular system in the root primordium was determined. It is relatively short and occurs in the first half of embryogenesis. The results obtained revealed no relationship between vascular system arrangement in root primordium and mature grain and mature embryo size.
3. Maize ear represents a type of inflorescence of which the apical part is delayed in development. Histogenically this uneven development becomes evident with the formation of a significantly lower mean number of poles in root primordia from the grains originating from the apical region of the cob. This is further evidence of the adaptibility of the vascular system development to environmental conditions.
4. As further causes of the variability in pole number those differences are considered which occur during sex cell formation, pollination and fertilization.

Measurements of the size of the nuclei of dioecious plants showed that the nuclei of male and female plants differ in agreement with the larger quantity of chromatin. The male. plants ofRumex acetosella andMelandrium album had larger nuclei, their Y chromosome being larger than the X chromosome, the same is true forRumex acetosa where the Y chromosome is smaller but there are two in the set.Ginkgo biloba had larger female nuclei because the Y chromosome was smaller than the X. The curves obtained by grouping all the nuclei of both sexes never had two peaks with regard to the small differences between the classes of maximum frequency.

In experiments from 1966-1968 a comparison was performed concerning the level of endogenous stimulators and inhibitors in leaves and shoots of peaches decapitated in three different times and in controls.
For the determination of these substances a biological test was employed after separation of the acid fraction of ethyl ether extracts by means of paper chromatography. Mathematical addition of total stimulations and inhibitions gave a new value, called "growth disposition" by the authors. Its graphical demonstration gives a simple curve which documents the growth rhythm of control plants as well as the response of plants to the time-regulated decapitation. In the case of shoots this response has always been positive,i.e. at all periods of sampling for analyses the growth disposition with decapitated plants was higher in comparison with controls.

Flowering in the short day plantChenopodium rubrum was inhibited by 5-fluoro-deoxyuridine (FDU) at a concentration of 4×10^-6 M and higher when applied during photoperiodic induction or immediately afterwards. This inhibition is always accompanied by a general reduction of growth (e.g. a decrease in the first leaf length). The mitotic activity within the shoot apex is completely blocked by FDU application during the photoperiodic treatment. The floral induction (evocationsensu Evans) was not cancelled in this situation as was revealed when reversing the FDU effect by thymidine application. One day after the end of the photoperiodic treatment (the plants were transferred to continuous light again) the FDU inhibition becomes irreparable. The results indicate that DNA synthesis and hence the mitotic activity are not obligatory prerequisites for photoperiodic floral induction inChenopodium. Low concentrations of FDU may promote flowering under suboptimal floral induction.

Flowering in the short-day speciesChenopodium rubrum L. was stimulated by treatment with abscisic acid (ABA) in concentrations from 1×10^-3M to 1×10^-7M only in plants partly induced by two dark periods. We assume that ABA weakens the inhibitory effect of continuous light (similarly as do some other substancese.g nucleic acid inhibitors) and thus enables the expression of the evoked floral state. ABA was ineffective in promoting flowering in photoperiodically non-induced plants.

Water potentials of leaves from well-watered plants were measured. There were species-specific differences in both the total and the osmotic potentials of pea (Pisum sativum), tradescantia (Tradescantia versicolor), rose (Rosa hybrida), bitter lemon (Citrus aurantium) and olive (Olea europaea). With tradescantia the potential measured after the destruction of turgor by freezing was less negative than before, a result which suggests that the value obtained is not identical with the real osmotic potential of the leaf. detached leaves of all species showed less negative water potential readings, and those of pea even a less negative osmotic potential, when cut into five pieces than when measured intact. Application of vaseline to the cut surface of the leaves reduced this effect with rose and olive, though not with tradescantia and pea. Measurements were also made of the water potentials of comparable leaves of tradescantia and bitter lemon, attached to and detached from their plants; when bitter lemon leaves were detached and watered through their petioles which protruded outside the thermocouple chamber, their potential became considerably less negative than when the same leaves had been attached to well watered plants. However, similar leaves whose cut petioles were introduced into the thermocouple chamber registered an even less negative potential.
The results are consistent with the hypothesis that when a leaf is cut off a plant, and even more so when it is cut into sections, the water previously held by matrix forces becomes available to dilute the "spilled" cell sap and to be absorbed by adjacent cells and thereby to increase their turgor and render the net water potential of the leaf less negative. Similarly, the apparent negative turgor of the succulent, tradescantia leaves is likely to be due to dilution of the osmotic component by cell wall water. The discrepancies between the readings of attached and detached leaves indicate a considerable whole-plant matrix component, and the results as a whole suglest that thermocouple psychrometer readings carried out on detached and even more on cut-up leaves may be artifacts and that it is desirable to determine water potentials on leaves attached to their plants.
The work was supported by a Government of Israel Fellowship and was conducted at the Department of Pomology and Viticulture, Faculty of Agriculture of the Hebrew University of Jerusalem, Rehovot, Israel.

Kind of substrate utilized by the respiration of mustard seedlings (Sinapis alba L.) was determined on the basis of found RQ values of control plants. This led to the study of the effect of 4-phenethylpyridine on relationships between lipase, lipoxidase, glycerolkinase and O₂ consumption: Enzyme activities and O₂ consumption rose from the second to the fifth day. According to these results, 4-phenethylpyridine increases degradation of storage fats in the beginning phase of fat catabolism, bringing about advantageous conditions for their metabolic utilization in plant, like in the case of saccharide metabolism.

1. The transfer of immature embryos from maternal plants to artificial media influenced the radial arrangement of vascular bundles in developing root primordia. The variability in the number of poles of the prospective protoxylem and protophloem, observed as a rule during embryogenesis under natural conditions, could not be suppressed even under the conditions ofin vitro cultivation. The possibility is admitted that when using agar medium the nutrient supply need not necessarily be equivalent for all embryos.
2. Using excised embryos of various ages the period of delimination of the vascular system in the root primordium was determined. It is relatively short and occurs in the first half of embryogenesis. The results obtained revealed no relationship between vascular system arrangement in root primordium and mature grain and mature embryo size.
3. Maize ear represents a type of inflorescence of which the apical part is delayed in development. Histogenically this uneven development becomes evident with the formation of a significantly lower mean number of poles in root primordia from the grains originating from the apical region of the cob. This is further evidence of the adaptibility of the vascular system development to environmental conditions.
4. As further causes of the variability in pole number those differences are considered which occur during sex cell formation, pollination and fertilization.

Red clover mottle virus isolated in Czechoslovakia was studied in relation to its reaction to varying temperature on primary French bean leaves (Phaseolus vulgaris L.) on which it forms local necrotic lesions. The plants were kept 24 or 48 h before, or 24 or 48 h after inoculation at the temperatures 23, 25, 27, 30, 33 and 36° C. After such exposures the French beans were kept at a constant temperature of 25° C. The lesions were counted at various intervals. In the experiment the optimal temperature for the maximum number of lesions seems to be 36 °C 48 h before inoculation. The temperature above 25° C applied 24 h after inoculation seems to have a decreasing effect upon the number of lesions formed by RCMV on primary leaves of French beans and the lesions appeared several hours later, especially at 30, 33 and 36° C. The temperatures 27, 30 and 33° C applied 48 h after inoculation have a further decreasing effect on the number of lesions. The temperature of 36° C applied 48 h after inoculation has an inactivating effect upon RCMV inoculated on French bean leaves and no lesions appeared 5 days after inoculation.

The incorporation of uridine-5-³H into shoot apices ofChenopodium rubrum, plants was studied using autoradiography. The evaluation of the rate of incorporation into the nucleolus and the extranucleolar part of the nucleus as a function of the total radioactivity in the apex yields quantitative data on the distribution of labeling in these parts of the nucleus. Incubation of intact germinating plants in uridine-³H makes it possible to carry out chase experiments.
Curves of uridine incorporation into the nucleolus and the extranucleolar part of the nucleus were obtained which demonstrated a non-linear course of incorporation. When incubating with uridine from 30 to 120 min the nucleolar/extranucleolar ratio of labelling was found to increase from 2 to 3. In chase experiments this ratio changed within three days from 3 to 1.
Interpretation of these results in view of the function of RNA localized in different parts of the nucleus is discussed.

First findings on the mutation efficiency of thermal neutrons in lentil are presented.
1) The highest proportion of segregating progenies with chlorophyll mutants and chimeric plants reached 22% when doses of 1.6 × 10¹² n cm^-2 and 2 × 10¹² n cm^-2 were used.
2) After irradiation with doses in the range from 2 × 10¹² n cm^-2 to 2.6 × 10¹² n cm^-2 different chlorophyll mutants were produced at the same time in 2 to 4% of the offsprings.
3) The maximum proportion of the progenies in which only the viridis mutants were segregated was 18%, that with xanthoviridis mutants alone 6%, with xantha 4%, with albina alone 2%, with chimeric plants alone 8%.
4) The highest number of various types of mutants together with various combinations of two types of mutants in the same progeny were induced by doses of 2 × 10¹² n cm^-2 and 2-3 × 10¹² n cm^-2.
5) The highest number of induced chlorophyll mutants per 1 offspring was 0.44 mutants after irradiation with the dose of 2.3 × 10¹² n cm^-2.
6) The highest number of chlorophyll mutants per 100 of planted seeds was 1.46 mutants after a dose of 3 × 10¹² n cm^-2.

Investigations were made on the effect of exposing barley seeds to gamma-radiation (5-40 kR), alone and in combination with the application of zinc (soaking the seeds in solutions containing 5.10^-5-5.10^-1% Zn for 12 hours before sowing) on growth and on the content of tryptophan, indole auxins and gibberellin-like substances in seven-day plants. Radiation decreased both growth and the content of tryptophan (e.g. by about 53% at 30 kR), of indole auxins (by about 60% auxin in the zone of IAA on the chromatogram at 30 kR), and also the content of gibberellin-like substances (by about 67% gibberellin content in the zone of GA₃ on the chromatogram) of plants. The irradiation of standard samples of tryptophan, indolyl-acetic acid and gibberellic acid alone with many times greater doses (up to 1000 kR) did not lead to marked radiochemical degradation of these substances. It can be assumed that radiation damages the enzyme systems "synthesizing" natural growth substances in plants. The damaging effect of radiation on auxins is already displayed in the synthesis of tryptophan, which is inhibited.
Zinc interacts with the damaging effect of radiation on growth. Optimum concentrations of zinc (5.10^-3% Zn) counteract the effect of radiation, up to doses of about 12 kR, on the growth in height in 7-day plants so that it is equal to the controls. Normal content of tryptophan and auxin in the position of indolecetic acid on chromatograms can only be reached by the addition of zinc when the dose of radiation was not greater than about 8 kR, which is less than the influence exerted by zinc on the restitution of growth. On the other hand, the biosynthesis of gibberellin-like substances at the position of gibberellic acid on chromatograms can be restored by zinc to their original level to doses of up to 30 kR. The increased biosynthesis of auxins and gibberellins caused by zinc in irradiated plants is explained by the activation of the remaining and non-damaged enzyme systems carrying out this biosynthesis. The activation of the biosynthesis of growth substances by zinc will also contribute to the restitution effect of zinc on the growth of plants from irradiated seeds.

Studies with gamma rays, fast neutrons, and EMS treatments in rice showed higher frequency of M₁ chlorophyll chimeras in the EMS treatments, a correlation between the frequencies of M₁ chlorophyll chimeras and M₂ chlorophyll mutants, and a higher M₂ mutation frequency in the progeny of chimerical M₁ plants compared to those of normal-looking plants.