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.

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.