The present report is focused on the study of participation of exogenous DNA in the process of postirradiation reparation of meristematic cells ofVicia faba primary roots. It is aimed at comparison of the positive reparative effect of isologous DNA with postirradiation action of heterologous DNA in its native, thermally denatured and DNAase-degraded forms, or DNA degraded by ultrasound, and with the effect of other biologically important macromolecules (RNA, histone, heparin, and dextran sulphate). For this purpose, the roots ofVicia faba irradiated by 150 r exposure were cultivated in solutions containing the above substances for an appropriate time interval. In squash slides both mitotic activity of the investigated cell population and frequency of postmetaphase chromosomal aberrations induced by radiation were evaluated. It was shown that a stimulation of cell division and reparation of chromosome damages were supported exclusively by isologous DNA. On the contrary, exogenously applied heterologous DNA increased postirradiation frequency of aberrations; maintenance of native structure of applied DNA was an essential condition for the above effect. Other macromolecules investigated on the course of postirradiation reparation ofVicia faba meristematic cells were without effect.

Physiological effects of volatile substances released by the overground as well as by the underground organs of higher plants were studied. The activity of the volatile substances was tested both when these substances were allowed to act directly in the air and when they were dissolved in water in the form of solutions. Plants which do not contain essential oils or which are not rich in them as well as those abounding in essential oils and other volatiles were used in the experiments. The physiological activity of the volatile substances was tested on rye seedlings.
The overground as well as underground mature organs of the tested plants were found to release volatile substances causing, when acting directly, in the majority of cases an inhibition of the growth in length and of the formation of dry matter in rye seedlings. A pronounced inhibition of the growth of rye seedlings was brought about especially by the volatile substances of "aromatic" plants such as common dill, wild thyme, yarrow milfoil, garden thyme, marjoram, etc. The volatile substances released by the organs of "non-aromatic" plants like sugar-beet, common sunflower, quackgrass, etc., were found to bring about a significant inhibition of the growth of rye seedlings, too.
The volatile substances released by the plant organs were found to be altogether absorbable in water and physiologically active also in the form of water solutions. With the exception of volatile substances from hemp and quackgrass leaves, which brought about a mild stimulation of the dry matter formation in rye seedlings, inhibitory effects of these solutions were found to prevail in all cases. Most effective were the solutions of the volatiles from some of the "aromatic plants".
An assay for olefines in the atmosphere of the experimental vessels demonstrated that in almost all cases ethylene is being released by the plant organs.

Changes in the variability of quantitative characters (number of fertile stems, length of the stem and of the spike, number of spikelets in the spike, number of seeds in the spike and in the spikelet) in M₂ induced with 0.1 mM, 0.2 mM and 0.3 mM N-nitroso-N-methylurea (MNH) and with 5000r and 10 000 r of X-rays inTriticum monococcum L. var.sofianumKörn. were evaluated. The mean of the populations remained practically unchanged by the mutagens whereas the variability increased considerably with increasing concentration or dose. Changes in the variability were more pronounced in the values for the first stem than in the values for the first three stems. When changes in the population mean were found (with some of the most elevated concentrations and doses), these changes were shown to be mostly due to a repetition of the cultivation, whereas the changes in the variability were mostly due to the action of the mutagens. In all experimental populations, mutations in quantitative characters were successfully induced.

Some biochemical properties ofTrigonella foenum-groecum infected withPeronospora trifoliorum have been investigated. Qualitative changes were observed in lipids, coumarins, amino acids and indole compounds only. A quantitative study of the phosphate content was also carried out. Neutral lipids did not show any significant changes. In addition to the fourteen phospholipid bands, the infected leaves contained a new band corresponding in R_f to phosphatidic acid or polyglycerophosphate. Seven coumarins were present in both the extracts. In addition 3-hydroxy coumarin, 5-hydroxy-4-methylcoumarin and 7-hydroxy-4-methyl-coumarin were detected in infected leaves. Higher levels of indole acetic acid and three of its derivatives were observed due to infection. Infection altered the free amino acid content. Tryptophan appeared and the total phosphate content increased. Increase in phenols and indoles suggest a higher respiratory rate whereas a higher content of inorganic phosphate suggests uncoupling of phosphorylation from respiration.

The shoot apex or fruitlets of Jonathan apple trees grafted on M IX rootstock and grown in pots in a greenhouse were exposed to¹⁴CO₂ in an assimilation chamber. The translocation of¹⁴C-labelled assimilates from treated organs to other parts of the plant was studied.
It was found that a very small amount of¹⁴C-labelled compounds was translocated from the shoot apex and very young fruitlets to the shoot stem. Preliminary chromatographic studies show that the chemical composition of the labelled substances detected below assimilation chamber differs profoundly from that of those remaining in the supplied leaves. The results support the view that there exists a translocation of some substances, possibly regulators from the sink to the donor.

Antonovka seedlings were obtained from the embryos soaked in abscisic acid (ABA) alone, gibberellin A₄₊₇, benzyladenine or the mixtures of these regulators. The inhibitory effect of ABA on the growth of the seedlings was of temporary duration. The height of the 12 week-old seedlings was dependent only on the degree of seed after-ripening and not on the ABA treatment.
The growth stimulators studied were unable to overcome the inhibitory effect of ABA observed in the early stages of seedling growth. The growth stimulators did not substitute, for cold treatment of apple seeds which is the only treatment so far known to overcome the dwarf conditions of the seedlings obtained from non-after-ripened embryos. ABA greatly suppressed the early stages of apple seedling growth (up to 6 weeks) during which they resembled physiological dwarfs.
The highest concentrations of ABA (2.0 μg ml^-1) greatly modified the root system of the seedlings, and produced a larger percentage of seedlings with unbranched roots.

Isozyme patterns and specific activity of ribonuclease (ribonucleate pyridinenucleotido-2'-transferase, E. C. 2.7.7.16) were followed in the extracts of segments from three growth zones of the root and in extracts of young and senescent leaves ofVicia faba L. Electrophoreograms of extracts from all three investigated root zones were identical, in the electrophoreograms of extracts from senescent leaves however one new ribonuclease occurred which could not be detected in the electrophoreograms of extracts from young leaves. Extracts from senescent leaves had higher specific activity of ribonuclease than extracts from young leaves. Extracts from the enlargement zone of the root and those from the maturation zone had a three times higher specific activity of RNase than extracts from the division zone.

The character of endogenous regulators in walnut buds was followed by means of bioassays in the course of vegetation. It was ascertained that a rise in the level of gibberellin-like substances precedes the sprouting of buds. The origination of new buds in the axil of young leaves is accompanied by a fall in the level of auxins, by a low gibberellin content and by the presence of inhibitors. In this situation the primordia of staminate catkins are diferentiated in the basal buds. The vegetative buds which are formed in the axils of further leaves, stop developing because of the accumulating inhibitors. Towards the close of vegetation the primordia of pistillate flowers originate in terminal buds and their differentiation is accompanied by a substantial rise in the level of auxin-like substances, while some of the inhibitors keep asserting themselves. On the basis of these findings we have tested the possibility of affecting the differentiation of staminate primordia and of vegetative buds by the exogenous application of selected regulators. Spraying young leaves with IAA and MH solutions will increase the number of vegetative buds in the twigs. A later spray of other twigs by TIBA and GA₃ solutions will increase the number of staminate buds.

Algae were cultivated in nutrient solutions containing nitrates or ammonium salts as the nitrogen source. We measured the culture density in the case of autotrophic and mixotrophic cultivation at different pH values, in the presence of nitrate also at different concentrations and in the absence of molybdenum. The dry weight and amount of nitrogen in the cells under these conditions were determined.
According to results obtained we conclude thatChlorella, in contrast toScenedesmus, prefers ammonia as the nitrogen source in the first growth period, later both prefer nitrogen from nitrates. Nitrogen from ammonium salts has a positive effect only during short-time cultivation. If glucose was used as a mixotrophic energy source (or perhaps H-donor), the unsuitability of ammonia as a nitrogen source was more marked. We suppose that the lower growth intensity of older cultures (i.e., after seven days) in ammonia medium is the result of the use of endogenous energy sources.
Both algae have adaptive systems making it possible to use nitrate nitrogen even in the absence of molybdate.

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.

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.

The meiosis of two mutants ofBrassica oleracea var.capitata was analysed which have been isolated after gamma irradiation and hybridization.
1. Univalents appear in different frequencies in the pollen mother cells of both these mutants attributed to a genetically conditioned reduction of the chiasmata frequency resulting in manifold irregularities in the later stages of microsporogenesis. The number of microspores per PMC varies between 1 and 8, the chromosome number of the microspores between 6 and 12. As a consequence of these meiotic disturbances a strong reduction of the fertility of male and female germ cells occurs.
2. In principle, both mutants show the same meiotic behaviour, but the irregularities appear in a stronger degree in mutant 45 as compared with mutant 47. They are obviously caused by the same mutated gene which shows differences in its manifestation in the two mutants due to their different genotypic constitution.
3. The mutant gene belongs to the group of desynaptic genes controlling the process of chiasmata formation. The degree of desynapsis caused by this gene is very weak as compared with ds-genes of other species.

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.

Effect of humus fractions on the toxicity of 2-methyl-4-chlorphenoxyacetic acid (MCPA) was examined in water cultures. Humus fractions and different MCPA quantities were added to Richter's nutrient solution used for maize (Zea mays L., cv. Kočovská raná) cultivation. The results show that MCPA and humus substances in the applied concentrations intensively influence the maize root system, especially the rhizodermis and apical meristem cells. MCPA reduces ion absorption, induces phosphorus excretion from root, reduces tissue hydratation and relatively quickly kills these cells, at the end stage and/or in the highest concentration. Humus fractions have an unambiguously positive effect on these processes, they increase the cell vitality. When humus substances are applied, the MCPA effect does not appear in potassium and nitrogen absorption, the inhibitory effect is maintained in phosphorus absorption and in tissue hydratation even with the most effective fraction-with fulvo acids. But all fractions increased the cell vitality of sorption tissue and meristems in the presence of MCPA.

The aim of the present investigation was to examine whether some of the growth defects of calcium-deficient pumpkin (Cucurbita pepo L.) seedlings are due to an incapability of the plants to assimilate nitrate nitrogen, such being the mechanism by which according to some of the previous authors growth defects in calcium deficient plants may be produced. The results of the present study, however, demonstrate that the accessibility of various possible products of nitrate reduction is not the limiting factor responsible for growth symptoms of calcium deficiency.

From the very continental high mountain basin Dasht-i-Nawor in Central Afghanistan an example of the daily course of some important ecological factors is given (irradiance, air, leaf and soil temperatures, water vapour saturation pressure deficit, evaporation rate, wind velocity) and some ecological characteristics (osmotic potential, refractive index and chloride content of the cell sap) of two species one of them being a facultative halophyte

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.

4-phenethylpyridin favours pentose cycle in glycide degradation inSinapis alba seedlings. The influence of the tested compound on following enzymes: hexokinases, saccharase, phosphorylase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphoglucomutase and phosphoglucoisomerase was studied. In roots of treated seedlings a substantial increase of pentose cycle enzymes was found together with the corresponding increase in glycide content. The increased activity of phosphoglucomutase may be explained by the chromatographically detected presence of stachyose in the seeds which as the source of galactose enables the formation of glucose-1-phosphatase.

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.

When studying the determination of nucleic acids in pollen based on extraction with hot 10% NaCl, further factors influencing the results were observed. Prolongation of the homogenization from 3 to 5 or 7 min caused considerable loss of DNA in extracts. On using trichloracetic acid to precipitate nucleic acids from the NaCl extracts, higher final values for the sum of nucleic acids were obtained than by precipitating with perchloric acid.

Our paper describes some morphological peculiarities ofMycoplasma bodies located in vascular bundles ofNicotiana glaucaGrah. and tomato infected with potato witches' broom disease. The influence of postfixation on the density of bodies and possible development of artifacts was studied in particular. It was found that bodies of adjoining cells may have a different shape. Also elementary bodies, approximately of uniform diameter, may occur in masses in close proximity to the cells containing "adult"Mycoplasma bodies. Deformed large bodies giving in a certain position the impression of "vacuolization" are evidently degenerated saucershaped forms. In addition toMycoplasma some other bodies with different inner structure were observed in the same cells.

The intact seeds ofPsoralea corylifolia which are actieually one-seeded fruit, presents a unique problem of dormancy. Germinability of these dormant seeds is not enhanced as a result of a number of treatments: 1) Dry-storage of 44 months under moderate conditions of the laboratory. 2) Periodic germination in different months of the year. 3) Immersion in ethylalcohol (70% and 100%), hydrogen-peroxide, nitric acid, acetone, ether solvent and hydrochloric acid. 4) Removal of pericarp.
Four distinct methods have also been evolved which effectively overcome the dormancy of the seeds: 1) Mechanical puncturing of seedcoverings. 2) Sulphuric acid treatment. 3) High temperature treatment. 4) Weathering of seeds.
Germination-behaviour of the latter 4 lots of seeds is compared and ecological significance of the reported dormancy mechanism is discussed.

The dynamics of the germination and formation of lateral roots under constant conditions were studied in pea Pisum sativum L., cv. Pyram. Various parameters of the above processes were evaluated statistically. The time at which the germination proceeds at the maximum rate was found to be 24.9 h from the start of the imbibition of seeds. The standard deviation of the germination time of an individual seed from the time corresponding to the maximum of germinated seeds was found to be 4.0 h. The formation of the lateral root primordia took place at 54.2 ± 2.9 h. At 73.5 ± 5.5 h from the beginning of the experiment, laterals on the surfaces of primary roots of seedlings became apparent. Differential curves of the distribution of the above processes were plotted graphically. The data obtained are valid for the given conditions and given experimental procedure. The methods described can be used in studies of primary root branching in various plant species.

The influence of GA and CCC on endogenous estrogens content in beans was investigated. The experiments were conducted in two variants analysing the amounts of estrogens 12, 24, 48, 96 h after application, and in the specific stages of plant development. The lack of influence of GA and the lowering of estrogens content under the influence of CCC was observed.

The intact seeds ofPsoralea corylifolia which are actieually one-seeded fruit, presents a unique problem of dormancy. Germinability of these dormant seeds is not enhanced as a result of a number of treatments: 1) Dry-storage of 44 months under moderate conditions of the laboratory. 2) Periodic germination in different months of the year. 3) Immersion in ethylalcohol (70% and 100%), hydrogen-peroxide, nitric acid, acetone, ether solvent and hydrochloric acid. 4) Removal of pericarp.
Four distinct methods have also been evolved which effectively overcome the dormancy of the seeds: 1) Mechanical puncturing of seedcoverings. 2) Sulphuric acid treatment. 3) High temperature treatment. 4) Weathering of seeds.
Germination-behaviour of the latter 4 lots of seeds is compared and ecological significance of the reported dormancy mechanism is discussed.

The budding capacity ofBegonia rex leaf fragments is well known; that of undetached leaves has been shown by us only recently after treating the leaves with 6γγ DMAAP. Benzyladenine is as effective as 6γγ DMAAP in stimulating budding. Lower temperatures (17°, 22-12°, 12°) are also capable of inducing bud formation but only after a small cut has been made in a main vein of the undetached leaf. Root formation can also be provoked on undetached leaves which have a cut in the main leaf vein by higher temperatures (24-22°) or by an IAA treatment. Differences in the first stages of bud formation on leaf fragments and on undetached leaves are observed using histochemical and histoautoradiographic techniques.

The mitotic activity of merstematic cells ofVicia faba, the frequency of chromosomal abnormalities and their interchromosomal distribution are evaluated in dependence on the concentration of maleic hydrazide (MH) and on the recovery period. The influence of exogenous DNA of different genetic origin on the course of repair of primary root cells damaged by MH was also studied. Isologous DNA which exhibited a strong repair effect in authors' previous experiments was quite ineffective in the case of maleic hydrazide. Heterologous DNA, on the other hand, had to some extent a parallel effect with MH in breaking down the structural integrity of chromosomes and increased the frequency of aberrations induced by maleic hydrazide in meristematic cells ofVicia faba.

Excised anthers ofNicotiana tabacum L. were culturedin vitro at the stage of pollen tetrads, which proved in our experiments to be the most suitable initial stage for cultivation, up to the stage of mature pollen grains, using Ito and Stern's nutrient medium, or this medium supplemented with uracil. Germinating capacity of the pollen grains formed and the lengths of pollen tubes were quantitatively evaluated.

Embryogenesis occurred in carrot root callus (Daucus carota L.) cultivated on simple synthetic medium containing IAA and 2,4-D. Embryoid development continued also during successive years when the tissue was cultivated on the same nutrient medium without those substances. Sometimes production of plants with atypical leaves was also observed. In those plants development of adventive embryoids occurred repeatedly. Result of this work confirmed reports about the organogenic potentiality of this species and about its sensitivity to some chemical substances.

A study was performed on the influence of obligate parasitesErysiphe graminis Dc. andPuccinia hordeiOtt4 on peroxidase activity in barley leaves, namely in both susceptible and resistant varieties. Attention was also paid to peroxidase activity in a susceptible wheat variety infected withPuccinia striiformisWest.
The following results were obtained:
In leaves of wheat and harley plants an enzyme was revealed which oxidized pyrocatechol and guajacol only in the presence of hydrogen peroxide. This enzyme can be inactivated by heating and strongly inhibited by cyanide. Evidently peroxidase is concerned.
Peroxidase in susceptible varieties of wheat and barley is markedly activated after infection with parasites mentioned above, this activation reaching maximum at the periode of parasite sporulation. On the other hand the barley varieties resistant toE. graminis andP. hordei, exhibit only a slight or no increase in peroxidase activity at this period. Thus we come to the conclusion that peroxidase does not probably appear to be the cause of the resistance of these varieties. It seems that in tissues attacked by obligate-parasites the intensity of its activation can be a result of the infection intensity.