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.

For three consecutive years the content of natural stimulators and inhibitors was observed in leaves and shoots of peach trees. Research was directed to the question of development of flower buds.
The substances under study were isolated from the acidic fraction of ether extracts by means of paper chromatography and their concentration was determined by biological test. The activities of substances which either stimulate or inhibit the growth of oat coleoptiles, were added up. The curve expressing the content of stimulators in shoots in relation to the fresh weight showed its maximum in the period of full growth of shoots (15 June-15 July according to the fluctuating vegetative conditions) and it showed a decreasing tendency at the end of the season. The decline of the curve showing the content of inhibitors is of similar direction but less steep. The trend of substances under study is the same in leaves as in shoots, but their quantity is lower. Stimulation and inhibition effects in individual sampling intervals were added up to make a common curve which seems to express the combined action of stimulators and inhibitors in the plant, which determines its growth pattern.

Der Verlauf von Brdička's serologischer Reaktion bildete ein Beschädigungskriterium der VersuchspflanzeSinapis alba L., die durch folgende Herbizidstoffe behandelt wurde: 2,4-D; 2,45-T; MCPA; Atrazin; Aminotriazol; 4-Phenäthylpyridin in den Konzentrationen 10^-3M, 10^-4M und 10^-5M. Während der polarographischen Bestimmung bewirkten die pathologischen Veränderungen der Pflanze verschiedene Höhen der katalytischen Eiweissdoppelstufen. Bei der oszillopolarographischen Bewertung kam es mit steigender Beschädingung zur Ausgleichung der Einschnitte der Kurvenabhängigkeit dE/dt=f(E). Die benützten Methoden zeigten grösste Veränderungen bei den Derivaten der Phenoxyessigsäure-was den stärksten Beschädigungen der Versuchspflanze entsprach.

Tomato and pear fruit underwent shifts in respiratory metabolism (CO₂ evolution) when ripened at reduced relative humidity (15 to 25% R.H.). A bimodal respiratory spectrum was observed with fruit ripened at low relative humidity; concomitantly, a number of the ripening indices were observed to quantitatively (mainly intensification) and perhaps qualitatively differ from fruit ripened at 80 to 90% R.H. The results suggest that the additional climacteric respiratory burst is coupled to metabolic changes associated with ripening and illustrate the dramatic influence water vapor deficit can have on physiological processes such as ripening.

The structure of the maize root enables one to determine the experimental specific conductivity of conducting and non-conducting tissues for the longitudinal water transfer. Using the method of Farmer and Berger in Huber and Schmidt's modification, successive differences in orders of magnitude were revealed among the experimental specific conductivities of the tissues of pith, cortex, and those of the area with concentrated xylem. The highest values of specific conductivity (cm³ cm^-2 h^-1 at 400 mbar per 5 mm distance, at 20° C) were determined in the area with concentrated xylem (mean value 10 018 cm³ cm^-2 h^-1); in the cortex area values by one order of magnitude lower were obtained (mean value 1 206 cm³ cm^-2 h^-1); in the pith area by two orders of magnitude lower (mean value 167 cm³ cm^-2 h^-1). The tissues of the area with concentrated xylem participated in the experimental root conductivity by 72 per cent, cortex tissues by 27 and pith tissues by one per cent. In this paper the individual tissues of maize root are characterized in detail from the anatomical viewpoint and the possible causes of the differences are discussed.

Pricking one of the cotyledons of aBidens pilosus L. (var.radiatus) seedling decapitated just above the cotyledons four times in succession induces after one minute the dominance of buds on the unaffected side.

Positive linear correlation between the resistance to water transport in liquid phase and water saturation deficit (w.s.d.) in the tissue ofBrassica oleracea andNicotiana tabacum leaves was observed. At the same values of w.s.d. corresponding values of the resistance to water transport were higher when dehydration of the leaf tissue occurred during the experiment and lower when water balance was in equilibrium or resaturation of the leaf tissue occurred.

The intensity of water uptake by halves of splitroot cuttings fromColeus blumeiBenth was measured by potometrical method. Inhibition of the water uptake induced by application of high concentrations of sodium salts of α-naftylacetic acid (NAA) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) in the treated half of the root induced an increase of water uptake by the other half. The compensation is not complete. If only one half of the root treated by synthetic auxin was allowed to take up water, MCPA appeared to induce a smaller degree of reversibility than NAA.