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.

Experimental Study of changes in water content during dehydration and rehydration of the Fern: Notochlaena vellea R. Br.-This study takes place after studies made on otherPolypodiaceenFerns. We have shown that, in these ferns, the survival duration was longer for the subterranean organs than for aerial ones. The problem was to show that this difference is due to a lower dehydration of the subterranean tissues. As far as we looked at the total water deficiency, we did not find any significant difference between the leaves and the meristematic parts of the subterranean organs: the main difference is the rate of rehydration which is higher in subterranean parts.

The effect of isologous DNA on the course of postirradiation reparation of meristematic cells ofVicia faba primary roots was studied in detail. A considerable interest was devoted to determinations of fundamental qualitative and quantitative conditions of the above effect of isologous DNA. Main criteria of the effect were both mitotic activity of irradiated cellular population and dynamics of chromosome aberrations induced by radiation. One set of experiments compared the course of reparation as occurred in regard to applied dose of ionizing radiation in native isologous DNA, DNA denaturated by heat and degraded by DNAase, and post-irradiation reparation of induced damages was favorably affected by native isologous DNA only. Another set of results evaluated the dependence of positive reparative effect of native isologous DNA on the length of the molecule demonstrating that in the process of reparation the presence of a complete DNA macromolecule was not essential. The last experimental group was focused on observations on the dependence of the rate of native isologous DNA effect on concentration of applied solution of the macromolecule.

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.

Time doses of a single concentration of streptomycin and its concentration doses acting for the same time period in a liquid medium had different effects on three strains of chlorococcal algae. This concerned both the physiological responses and permanent changes in the characteristics of cell colonies growing from treated cells. Significant differences were recorded in: the number of autospores produced during the first division of the treated cells on the surface of a solid medium, the length of the lag phase, the growth rate of the diameter of cell colonies, and the survival of the treated cells. The permanent changes in the characteristics of the growing colonies were very different in the individual algal strains in quality and frequency. Physiological and the mutation effects were compared and discussed.

The effect of isologous DNA on the course of postirradiation reparation of meristematic cells ofVicia faba primary roots was studied in detail. A considerable interest was devoted to determinations of fundamental qualitative and quantitative conditions of the above effect of isologous DNA. Main criteria of the effect were both mitotic activity of irradiated cellular population and dynamics of chromosome aberrations induced by radiation. One set of experiments compared the course of reparation as occurred in regard to applied dose of ionizing radiation in native isologous DNA, DNA denaturated by heat and degraded by DNAase, and post-irradiation reparation of induced damages was favorably affected by native isologous DNA only. Another set of results evaluated the dependence of positive reparative effect of native isologous DNA on the length of the molecule demonstrating that in the process of reparation the presence of a complete DNA macromolecule was not essential. The last experimental group was focused on observations on the dependence of the rate of native isologous DNA effect on concentration of applied solution of the macromolecule.

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.

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.

Young seedlings ofZea mays L. andCucurbita pepo L. were grown in water culture with a layer of oil (linum or olive oil) or liquid paraffin. The seedlings transport oil and parafin into the top and in the young root.Cucurbita seedlings proved to be very sensitive and died within few days.Zea proved to be resistant. InZea this transport of oil was found to be related to the age of the seedlings and the zone of the root in contact with oil. The oil was localised in the cell walls of different tissues of root and top, in the intercellular spaces of cortex and pith and in the xylem vessels.

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.

Five different isolates of beet yellows virus were maintained without any changes in their properties onTetragonia expansaMurr. syn.T. tetragonoidesPall. for a long period of time. According to their characteristics and different properties especially in a diploid inbred line of sugar beet the isolates are considered to be strains of BYV and are classified into three groups: group of mild strains (the mild masked and mild strains), normal strains (the common strain) and necrotic strains (the severe necrotic and necrotic strains). The necrotic strains of BYV were relatively easily transmissible manually to sugar beet plants and other indicator species. The common strain can be transmitted to sugar beet,Chenopodium quinoaWilld. but not toC. capitatumL. Asch. Mild strains are transmissible with difficulty andC. quinoa is the only species which develops a larger number of local lesions after inoculation. In contrast to the mild masked and common strains it is manually transmissible toC. capitatum. The mild masked strain can not be transmitted to sugar beet.Nicotiana quadrivalvisPursh. is not susceptible to mechanical inoculation with BYV. Aphid transmission withMyzus persicae (Sulz.) was positive in experiments with necrotic strains only. Mechanical transmission of BYV was successful also toC. foliosum(Moench) Asch.,C. murale L. andClaytonia perfoliataDonn. The last two species were susceptible to inoculation by aphids as well. Attempts to transmit the virus manually toT. expansaMurr. andC. giganteumDonn. failed.

Seedlings can be used to predict field resistance, if any, of wheat varieties and experimental lines to wheat powdery mildew fungus,Erysiphe graminis f. sp.tritici. First leaves of 8-day-old seedlings of a field-resistant wheat showed a greater frequency of primary infections in subsidiary cells of stomata than those in a susceptible wheat. This method of predicting field resistance of experimental lines from seedling studies should prove time-saving because crosses involving field-resistant experimental lines can be made in the same generation.

Barley seeds were treated with ethyl methanesulphonate (EMS) for 3 h at 25° C, washed with tap water for 24 h at 25° C, redried at 40° C to different moisture contents below 15% and stored at 25° C in desiccators or in sealed plastic bags. The criteria used for expressing the effect of storage were the M₁ seedling height and the frequency of chromosomal aberrations. With 14.9% seed moisture a strong increase of biological injury occurred in the course of a 2-week storage, while storage of seeds having an initial moisture content of 11.7% led to a significant increase of injury only after 6 weeks. Superdry EMS-treated seeds with 5% or less moisture can be stored at 25° C without any changes in the biological effects. A method is recommended to avoid the EMS-storage effects.

Five strains of cucumber mosaic virus (CMV) were distinguished in the isolates of viruses which attack cucumber in Czechoslovakia (Havránek 1970). The strains A, B, C, D, and E of CMV were defined according to different syndromes onNicotiana tabacum L.,N. glutinosa L.,Phaseolus vulgaris L. andChenopodium polyspermum L. The Czechoslovak strains, in comparison with American ones, did not cause systemic disease inCucumis anguria L. orCucurbita moschataDuch., but strains D and E of CMV suppressed the tolerance of American cucumber cultivar Wisconsin SMR 18. The propertiesin vitro of isolated CMV strains correspond to the description of CMV, but we did not succeed in establishing their antigenic behaviour. The relation of the Czechoslovak CMV strains to those described in publications is discussed.

A procedure was developed for satisfactory freeze-sectioning of root tips. The use of Ca formol-fixed material kept and frozen in Holt's syrup is recommended. The existence and different localization of 2 fractions of non-specific esterase was verified in root tips ofVicia faba. The same results were revealed in fixed and unfixed material. The dynamics ofin situ reaction was followed with respect to optimal incubation time. The results with substrates of different chain length support the existence of 2 fraction of the studied enzyme, none of which, concerning substrate specificity, is a lipase. It follows from the present studies inVicia faba and other species (Cucurbita pepo, Lupinus albus, Pisum sativum Zea mays), that non-specific esterase localization is not directly given by histogenesis.

A simultaneous azocoupling reaction used for in situ localization of non-specific esterase may be applied even for quantitative in vitro measurements. The developed standard procedure was verified with regard to substrate concentration, inhibitory effect of diazonium salt, incubation time, stability of resulting dye, relation between the amount of dye and the amount of material. On HW medium, non-specific esterase activity increases considerably both in phloem and xylem explants from Daucus carota L. taproot. The increase of enzyme is higher and appears earlier than the increase of fresh weight and dry matter, especially in the explants of phloem.

Some methods were studied which use hot 10% NaCl solution for the extraction of both RNA and DNA from pollen. The raw salt extracts were precipitated with perchloric acid, trichloroacetic acid or ethanol and purified according to the described methods. The nucleic acid hydrolysates were obtained in several ways. In all the samples spectra in the UV-region were measured and the nucleic acid contents were determined according to the absorbance at 260 nm. In order to ascertain the extent of contaminants, the contents of phosphorus, saccharides and proteins were determined. It was found that by the methods studied it is possible to remove some impurities from extracts, but that the extractions of nucleic acids from pollen are not quite quantitative. A part of nucleic acids remained unextracted after the salt extraction in pollen, but it was possible to obtain it only by an additional extraction with 1 N perchloric acid at 75°C.

When cytokinin 6-(γ,γ-dimethylallylamino)-purine-8-¹⁴C was injected into the side root of a one-year-old apple graft, variety Cox's Orange Pippin, it was mainly transported acropetally, but a certain part of the radioactivity was also transported basipetally into the root below the place of injection. 6 days after application of the labelled cytokinin most of the radioactivity was detected in the xylem, 20-30 cm above the place of application. An appreciable quantity of radioactivity was transported toward the apical part of the plant as far as 100 cm from the point of application. Special analysis showed that 6 days after exposition about half of the remaining radioactivity was present in 6-(γ,γ-dimethylallylamino)-purine-8-C¹⁴ and the rest went to the other metabolites. The cytokinin was transported acropetally mainly in the transpiration stream.

Actual heterogeneity of indicators of water balance was studied on tissue segments from leaves ofBrassica oleracea L. v.acephala andNicotiana tabacum L. under controlled conditions. Maximal values of transpiration rate, water absorption rate, water transport rate and low values of WSD at the same time were observed at an initial WSD of 0% in segments from middle leaves and at an initial WSD of 20% mostly in segments from upper leaves. Although the properties of leaf tissue itself were probably the basic factors determining the actual heterogeneity of indicators of water balance, without connection with all other factors (e. g. various microclimates, supply of water) heterogeneity did not appear to a full degree.

In rooting poplar shoot cuttings of identical morphogenetic characteristics at the same time, the author succeeded to evoke differences in the radial arrangement of the vascular system by different environment influences. More favourable rooting conditions in the green-house, when comparing with the less favourable field conditions, caused root formation with a higher number of alternating xylem and phloem poles. The representants observed (I 214,Populus deltoides var.monilifera, P. pyramidalis) did not react in the same way on the different onvironment. The hybrid I 214 was the most sensible.
It was also possible to induce differences by indoleacetic acid (IAA) exogenous application. Not only the number of the roots formed increased in a highly significant manner in the cuttings influenced by IAA, but also the number of poles in the radial vascular bundles of the induced roots was higher in a highly significant way.
From the results given above it can be deduced that external conditions affecting activation of dormant root primordia in poplars influence also the pattern of vascular tissue differentiation in formed roots.

When cytokinin 6-(γ,γ-dimethylallylamino)-purine-8-¹⁴C was injected into the side root of a one-year-old apple graft, variety Cox's Orange Pippin, it was mainly transported acropetally, but a certain part of the radioactivity was also transported basipetally into the root below the place of injection. 6 days after application of the labelled cytokinin most of the radioactivity was detected in the xylem, 20-30 cm above the place of application. An appreciable quantity of radioactivity was transported toward the apical part of the plant as far as 100 cm from the point of application. Special analysis showed that 6 days after exposition about half of the remaining radioactivity was present in 6-(γ,γ-dimethylallylamino)-purine-8-C¹⁴ and the rest went to the other metabolites. The cytokinin was transported acropetally mainly in the transpiration stream.

The formation of the protein complex during barley grain maturation is characterized by unequal synthesis of different protein fractions. In ten day-old grain the dominating protein is glutelin, followed by albumin and globulin. The content of prolamin is at this stage negligible. Particularly after the eighteenth day of maturation intensive synthesis of prolamins begins, which continues during the entire maturing period in almost the same ratio as total N accumulation in the grain. From the twenty-fourth day the amount of prolamins exceeds that of glutelins, and at full maturity 50% of the proteins are prolamins. The glutelin content increases absolutely, but relatively it decreases from 41 to 26%.
The amino acid composition of flour from total grain as well as the amino acid composition of the individual proteins is significantly changed during maturation. Generally the changes are manifested in an increasing content of Glu and Pro and a decreasing content of Asp, Ala and Lys. These changes seem to occur as a result of an increasing representation of prolamin, which is characterized by large content of Glu and Pro and low content of Asp, Ala and Lys compared with other protein fractions.

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.

Callus tissues were derived from the stem of healthy tomato plants (Lycopersicum esculentumMill. ev. Průhonické) and of plants infected with potato witches' broom-a disease caused by mycoplasma. Callus cultures were established on modified fully synthetic media described byMorel (1948) and byMurashige andSkoog (1962). Callus cultures obtained from diseased plants were grown and subcultured on both media, growth in primary isolates from healthy plants took place on the Murashige and Skoog medium only. Growth of callus tissue derived from diseased plants was more vigorous even after several subcultivations in comparison with callus tissues isolated from healthy plants. Variations in the morphology in these callus cultures were not noted. Callus cells of diseased plants varied in size; they were about 50% larger than those from healthy ones. Implantation of primary and subcultivated callus tissues into tomato stems of healthy plants did not show any symptoms of infection on test plants.