"Euonymus mosaic virus", purified from cucumber cotyledons by the differential and density-gradient centrifugation, shows typical nucleoprotein absorption spectrum. Electron microscopy reveals isometric virus particles of about 37 nm diameter. No reaction of purified "Euonymus mosaic virus" was observed with antisera against a raspberry ringspot virus, tobacco ringspot virus, cherry leaf roll virus, strawberry latent ringspot virus, tomato ringspot virus, elm mosaic virus, arabis mosaic virus, tomato bushy stunt virus and watermelon mosaic virus.

The content of naturally occurring free substances with cytokinin activity was investigated in growing apices of apple shoots during the vegetative period. In the end of May one substance with cytokinin activity was found. During the first period of growth activity we found three such substances with more hydrophobic behaviour and in the culmination of the second period of growth activity we found other three or four substances displaying on the chromatogram more hydrophylic behaviour.

A technique for studying the water relations of fleshy fruits such as strawberry by measuring the beta ray penetration through the tissue is described. As a source of beta radiation, an active preparation of³²P melted into a capillary glass tube was used. The technique described permits a study of the changes in the water content of fruitsin vivo.

The effect of acute gamma rays (⁶⁰Co; 1 to 10 kR) on the vascular differentiation in stems of seedlings of Capsicum annuum L. long fruited cultivar at 8-loaf stage of development. Prooambium, phloem and xylem of irradiated seedlings showed an early initiation and maturation in terms of distance from the tip. Magnitude of these differences increased with the increasing exposures and time following irradiation. In irradiated seedlings there is a ohange in the developmental sequence of metaphloem and metaxylem when they first appear (in terms of number of leaf primordia). There is also a general increase in the number of procambial cells, sieve elements and vessel elements after irradiation.
The early initiation and maturation of the vascular tissue is correlated with the growth inhibition resulting from cell death and suppression of cell division activity in the shoot apex.

Free and bound gibberellins were estimated in individual leaves of winter wheat using TLC a lettuce hypocotyl bioaasay. Bound gibberellins were extracted from the hydrolyzate of the water remnant after the removal of free gibberellins.
Each leaf exhibits its own dynamics of free and bound gibberellins during its individual ontogeny, the gradual changes tending to be identical in every leaf. In young developing leaves the level of free gibberellins is high and that of bound is low. Further, inhibitors are sometimes present. The free gibberellin level rises with the activisation of growth and vital activity of a given leaf. Towards the end of the life cycle the content of free gibberellins is reduced to its minimum and inhibitory substances appear. The dynamics of bound gibberellins is opposite to that of free ones during ontogeny.

Using four independent late mutants, obtained by treatment of the early cultivar Dijon-G with N-methyl-N-nitrosourea, it was found that their delayed flowering has a monogenic genetic basis, the mutant alleles appearing to be incompletely dominant. All these mutants display a positive reaction to the graded vernalisation; the vernalisation requirement of the individual mutants is, however, both quantitatively and qualitatively different and hence specific for each of the mutant genotypes. lodoacetic acid is found to inhibit the vernalisation of the mutants to some extent only when the duration of the vernalisation is relatively short (20 days). A hypothesis is advanced, assuming a potential existence of a complete genetic apparatus for vernalisation already in the Dijon-G cultivar, where it is, however, blocked by suppressor or epistatic genes.

Using the phenol extraction method and MAK column chromatography the contents of nucleic acids in styles ofNicotiana alata were estimated before and up to 48 h after compatible pollination. As a result of pollination, high-molecular-weight rRNA and DNA registered a significant increase in their content approximating 30% and 16% respectively. The change in sRNA (4-S tRNA and 5-S rRNA) level was very slight and non-significant. In pollen grains there is an unusually high amount of rRNA with respect to the content of other nucleic acids and the rRNA/tRNA ratio approximates 14 : 1. On the other hand, in non-pollinated styles the content of rRNA is only about 6 times higher than that of tRNA. The changes in nucleic acid level found in styles after pollination are at least in a major part the result of the addition of the nucleic acids present in the amount of pollen used for pollination. The high rRNA level relatively to tRNA being generally associated with rapidly growing cells, its significance in pollen may be related to the rapid growth of pollen tubes.

The new growth promoter, N(2-acyl-l,3-indane dione) triethylammonium iodide (L-TEAI) enhanced the elongation of the seedlings of cluster bean (Cyamopsis tetragonoloba (L.) Taub, belonging to familyPapilionaceae). When the two growth regulators, L-TEAI and cycocel were applied together, the cycocel induced inhibition of radicle elongation was reversed, but it failed to reverse the inhibition of hypocotyl elongation.

The course of androgenesisin vitro was investigated with anther cultures of two chlorophyll mutants of Nicotiana tabacum. A different sensitivity to the hormonal composition of the medium was revealed between the cultures White Seedling and Sulfur; the stimulatory effect of kinetin on the frequency of androgenesis was observed only in White Seedling cultures. In addition to green plants, "aurea" (mutation Sulfur) or "albino" (mutation White Seedling) phenotypes also differentiated in both cultures. The possible causes of variability in the participation of green and mutant forms are discussed.

Ultrathin sections were prepared from the tissues of lettuce leaves with mosaic-like symptoms and thickened nervature which were studied by means of electron microscopy. Intracellular inclusions surrounded by a membrane were found in the cytoplasm of parenchym cells of the investigated lettuce leaves(Lactuca saliva L. provar.capitata L. nid.jaggeriHelm., cv. Pražan). Crystals with a distinctly apparent hexagonal lattice could be observed in the inclusions. No crystal containing inclusions were found in the tissues from the leaves without mosaic-like symptoms and in those from thickened nervature.

Changes in the transpiration rate of intact spring barley plants, cv. "Slovensky dunajsky trh", were studied separately in the light and in the dark under controlled temperature and illumination, after the infection withErysiphe graminis DC, during an 8 day period of the development of the fungus. In the first stage of pathogenesis, the fungus diminishes water output from the host plants in the light. An opposite phenomenon can be observed in the dark; water output from infected plants in the dark increases sharply mainly in the stage of advanced fructification. Thus, the fungus considerably diminishes the ratio of water output from the host plants in the light to that in the dark.

In water soaked barley seeds the respiration rate (QO₂) at 25 °C is about 100 times higher at 30% than at 20% water content. The treatment of seeds with mutagenic methyl methanesulphonate led to the depression of the respiration rate in dependence on the applied mutagenic dose. Seed storage at 30% water content resulted in a recovery from the inhibition of seed respiration caused by methyl methanesulphonate. In contrast, at 20% seed water content the respiration rate either slightly decreased or remained unchanged in the course of storage. The results are discussed in relation to the previously described changes in the yield of induced mutagenic effects in barley seeds treated with monofunctional alkylating agents and stored at 30% and 20% seed water content.

Ethylene was collected in methanol solution of mercuric acetate and the addition compound formed was then separated by means of paper chromatography. The spot area and colour intensity after detection were determined using a densitometer. The amount of collected ethylene was calculated from a calibration curve.
The ethylene liberated from plant samples was collected during one or two days. During this period the amputation of the whole plant organs did not influence ethylene production. Changes in ethylene production were found after segmentation of the tissue or after the treatment with auxin and Co²⁺ ions.
The above-ground parts of investigated herbs released 0.3 to 3.5 μl of ethylene per kg fresh weight per hour. The leaves of investigated trees released 1 to 20 μl of ethylene per kg f.w. per hour. The rate of the production of ethylene seems to be specific for a given species.

Unmetabolized nitrite occurs in 3 cm long apical segments of primary pea roots(Pisum sativum L., cv. Raman), isolated from 6 d old seedlings, grown under aseptic conditions for 10 h in nutrient solutions containing 0.1 to 2 mM nitrite concentration, its amount being dependent on the concentration in the nutrient solution. With increasing amount of nitrite in the roots, the ratio between NAD⁺-GDH₁ and NAD⁺-GDH₂ isoenzymes is changed without influencing significantly the total NAD⁺-GDH activity. After 48 h cultivation unmetabolized nitrite occurred in the roots only in small amounts and the ratio of activities of these isoenzymes was not affected significantly. NADP⁺-GDH activity, detected in the gels at the same site as NAD⁺-GDH₁, was depressed by increasing nitrite concentrations.

The experiments showed that after gamma irradiation as well as after irradiation by secondary cosmic rays (hard component)Equisetum arvense spores produce in the first developmental phases prothalia at a changed rate,i.e. in favour of the females. This effect being specific for radiation cannot be produced by heat, pressure or changes of electric and magnetic field (i.e. factors appearing in higher sea levels with a stronger intensity of cosmic rays). It will be possible to apply the sensitivity of the mentioned method for investigating the problems of testing cosmic ray variations. The possibility of its application in spontaneous variability research is not less important.

Fusarium solani (76%),Phyllosticta phaseolina (12%) andAspergillus flavus (10%) were isolated from bean(Phaseolus vulgaris) seeds showing lesions. Out of these the first two caused 30 per cent and 20 per cent seed rotting respectively after artificial seed inoculations. When inoculum was added into the soil before sowing the seed, 35 per cent and 10 per cent pre-emergence rot ocurred and there was 35 per cent and 15 per cent post-emergence blight when soil with healthy seedlings was inoculated withF. solani andP. phaseolina respectively.F. solani caused similar lesions on bean seeds when inoculated after an injury.F. oxysporum was isolated from the roots of dried bean plants showing necrosis.

The dependence of ethylene production and respiration rate on the concentration of gibberellin (GA) applied in water emulsion of lanoline to young fruits was studied in Yellow transparent apples. Ethylene production and respiration rate were slightly increased by GA treatment. The increased level was maintained throughout the entire ripening period, which was also apparent from the total amount of both released gases. A gas-chromatographic method, using a flame ionization detector for simultaneous determination of ethylene and CO₂ in the atmosphere of experimental biological containers, is described in this paper. CO₂ is hydrogenated to methan on Ni - ThO₂ catalyst by hydrogen which is used as carrier gas. The gases pass the hydrogenating reactor after the separation in the Chromatographic column before entering the detector.

The cytokinin activity of a group of derivatives of N-n-butyl-N'-arylthiourea and their effect on the uptake of amino acids and the accumulation of total nitrogen in seven-day barley seedlings have been investigated. It was established that N-n-butyl-N"-2,4-dinitrophenyl-thiosemicarbazide, N-n-butyl-N'-o-,m- andp-chlorophonylthioureas, N-n-butyl-N'-3,4-dichlorophenylthiourea and N-n-butyl-N'-2-methyl-4-ehlorophenylthiourea possess a high activity with respect to the retardation of the chlorophyll breakdown. Substances with a high cytokinin activity cause an increase in the amount of total nitrogen and amino acids, mainly of glutamic acid, aspartic acid and serine in the roots and loaves of seven-day barley seedlings.

Metabolism of dry mungbean seeds(Phaseolus aureus) was compared with that of 3 h imbibed ones. Respiration rates sharply increased upon imbibition which was accompanied by large water uptake. Storage protein was degraded resulting in the rise in soluble nitrogen. RNA and water soluble protein content increased but DNA declined. It is suggested that some of the soluble nitrogen pools are diverted to RNA formation which in turn produce enzyme protein. In mungbean seeds imbibition of water thus triggers a series of metabolic changes within 3 h with the respiratory energy as the driving force.

A study was made on certain problems connected with the application of methods of stigmatal and placental pollinationin vitro in the snapdragon.
Germinable pollen without microbial contamination could be obtained only from the flowers which were left, after surface sterilization, on the stem till the dehiscence of anthers. The germination of pollen, and especially the growth of pollen tubes was better in a 0.3 M lactose solution with 10^-3 per cent H₃BO₃ than in usual sucrose media.
The seedsin vitro could be obtained only after normal pollination and the successive artificial cultivation of the entire pistil (the method of stigmatal pollinationin vitro). The seeds did not differ either in their morphology or in their size from those developed under natural conditions, they were viable and without dormancy.
Though the pollinated pistils were cultivated in the medium without growth substances, callus formation from uncovered ovules and placenta was observed in some cases. A dependence was revealed of the proliferation on pollination and on the cultivar employed.
When using the method of placental pollinationin vitro we failed to obtain seeds. The main difficulty in the use of this method seems to consist in the fact that pollen tubes are not capable of growing from the surface of ovules and placenta into the micropyle.

The relationship between the water potential (Ψ_w) and the water saturation deficit (Δ W_sat) in kale and maize leaf tissue was measured during dehydration and resaturation either of leavesin situ or of cut leaves. The curves relating Ψ_w toΔW_sat were similar in all variants, but at the same values ofΔ W_sat corresponding values of Ψ_w were always lower in leavesin situ than in cut leaves and during dehydration than during resaturation.

The effects of temperature treatments on rice seeds in the early imbibitional phase were studied with respect to changes in germination percentage, seedling growth in terms of root and shoot lengths, water uptake, respiration and hydrolytic enzymes,viz. α-amylase, adenosine triphosphatase (ATPase) and phytase. As compared with the control, the treatment for 30 min at 50 °C caused a variable degree of increase in all these characters and a positive correlation existed between seedling vigour and hydrolase activities. The treatment for 30 min at 60 °C, on the other hand, elicited a retarding influence on these characters. As regards the enzyme activities, the damaging effect of 60 °C could, however, be visualized only after 72 h of germination which was preceded by an enhancement during the early hours.

A fully normal meiosis was found inAllium sativum L. by means of PMC analysis. Quadrivalents were formed only in several cultivars. The cultivation of inflorescence stem (after the exstirpation of bulblets) in a tetracycline solution of 900 i.u. induced a formation of fertile flowers. The first pollen mitosis was studied and the pollen parameters compared with those ofAllium cepa L. Evidence for the pollen sterility was given by crossings on sterile types. A microbiological factor was not isolated.

Mature seeds ofTaxus baccata L. andTaxus baccata L.fastigiata Loudon contain embryos which are both immature and dormant. Embryo cultures were carried out in order to test the relative effciency of gibberellins (GA₃ and GA₄), chilling and leaching. The increase of germination percentages depends on the treatment applied and the tested variety. WithTaxus baccata, the germination of which is very difficult, a double treatment either leaching and gibberellins or leaching and chilling are necessary to obtain a high percentage of germination. Our results are compared with facts already known on mature dormant embryos of other plants.

The high M₁ sterility is the factor limiting the increase of the mutation frequency after treatment with nitrosamides like N-methyl-N'-nitro-N-nitrosoguanidine, N-methyl-N-nitrosourea, N-methyl-N-nitrosourethane and N-ethyl-N-nitrosourethane, whereas for ethylvinylnitrosamine-treatment the limiting factor is the toxic action on the M₁ seed germination. The decrease of mutation frequency at high dimethylnitrosamine doses is explained by the inhibition of enzymes or enzyme-like system which hydroxylate nitrosaminesin vivo and thus enable the production of a mutagenic alkylating intermediate. The increase of mutation frequency after treatment with X-rays is limited both by the decreased M₁ survival and M₁ fertility.

Three strains of three different species of chlorococcal algae(Chlorella kesslerii Scenedesmus quadricauda andScenedesmus obliquus) were compared in their physiological and genetical responses to N-ethyl-N-nitrosourea (NEU). The mutagen was applied in the basic doses corresponding to their specific tolerance to it. Exponentially-graded doses derived from the basic ones acted for the same period of time and single basic doses acted at linearly-increased periods of time in parallel experiments. The influence of the mutagen on the cell cycle just in progress was characterized by the increase in the frequency of cell divisions which yielded a lower number of autospores. The conditions of the cells during the first three days after treatment were determined according to the average increase of their lag phase. The relative toxicity of the mutagen was expressed as the survival frequencies. The mutation effects were evaluated according to the frequency of permanent changes observed in the growing cell colonies : lethal, morphological and pigmentation. NEU was found to be a relatively suitable mutagen for the chlorococcal algae studied.