The frequency of nucleus and cell division in prothallia ofEquisetum arvense L. grown under aseptic, defined conditions shows a considerable stabillity in the course of long-term experiments. This stability can be impaired if germinating spores are afflicted in the period 50 ±5 h after sowing by the just occurring Forbush effect in the period of decreasing intensity of cosmic radiation but not in the period of its repeated increase.

5-aminouracil induces a partial synchronization of mitoses in barley, onion and garlic root tips. The highest degree of synchronization has been achieved in garlic where the mitotic index reached the value of about 36%, while in onion and barley the values equalled about 20%. The concentration causing the maximal synchronization in barley (400-750 ppm) was many times higher than in garlic (62.5 ppm) and onion (100 ppm). The occurrence of micronuclei was evaluated in garlic, under the conditions when synchronization was maximal. It was increased nearly tenfold as compared with the control.

[³H] DNA fromEscherichia coli and [³H] thymidine were applied, in sterile conditions, on isolated barley embryos and on roots excised from these embryos, both cultivated in the liquid medium and on halves of barley seeds, through the endosperm bridge. In embryos and roots, the labelled compounds were applied in 1.5% sucrose + 0.2 SSC alone, or together with either unlabelled thymidine or DEAE-dextran. Similar labelling indices were found after [³H] thymidine and [³H] DNA treatment which shows that the activity of [³H] DNA is utilized during the S phase. After application of [³H] thymidine, only cell nuclei in S phase were labelled. After the application of [³H] DNA an extranuclear label, in addition to the labelling of nuclei in the S phase, was observed in some experimental variants. The density of label above labelled nuclei after [³H] DNA treatment sharply decreased when unlabelled thymidine or DEAE-dextran was added, while the density of label above nuclei labelled by [³H] thymidine decreased when unlabelled thymidine but not DEAE-dextran was added. The labelling of nuclei with the label from [³H] DNA is the result of degradation of exogenous DNA reutilization of low molecular weight products. Extranuclear labelling is most probably due to the polymerous or partly degraded DNA.

Apparent photosynthesis (P_n) and root respiration (R_n) of 8 to 10 d old intact bean plants were studied separately at different temperatures and oxygen concentrations acting on the roots using IRGA technique. P_n is reversibly decreasing during 3 h root cooling (+ 5 °C) in accord with bending down of the primary leaves, and closing of the stomata. Plants adapted to low root temperatures show no effect of increasing the latter on P_n. Even 3 h oxygen deficit in the root medium has no influence on P_n but is increasing R_r in consequence of alteration in ' metabolism from respiration to fermentation. One must distinguish between short time reaction and long time adaptation of the plant on root stress.

The study of certain conditions for the extraction of seed proteins ofAllium cepa revealed that the best extractibility of proteins is obtained by the use of a buffered physiological solution at 20 °C in comparison with TRIS-glycine buffer at 5 °C. Using potassium phosphate buffer with 0.01 M mercaptoethanol and 0.4 M NaCl, an amount of proteins by up to 25 per cent higher passes into solution as compared with the physiological solution, but these extracts are unsuitable for the electrophoretic separation in polyacrylamide gels. The defatting of the seed meal under low temperature did not affect the qualitative composition of the protein complex studied, the addition of a 1 per cent soluble starch to the polyacrylamide gel. improved its resolution.

Studies performed on spring wheat (Triticum aestivum L. var.lutescens), cv. Kaspar and Kolibri revealed differences between cultivars in leaf dehydration tolerance. The differences were found to be responsible for the changes in plant growth and productivity observed under drought conditions. Thus, determination of leaf dehydration tolerance may allow the prediction of the plant response to the water stress in terms of plant growth and grain yield. Differentiated drought responses of both cultivars are described.

In isolated leaves ofBryophylluni crenatum the intensity of marginal bud formation decreases from the apex towards the blade base, which is associated with the decreasing content of enioganous gibberallins. As proved by Dostál (1930), the formation of marginal buds on transversely divided blade of the isolated leaf increases in comparison with the non-divided control leaf. The results of our experiments have revealed that the increase in the formation of marginal buds in the blade transversely divided into the apical, middle and basal parts is connected with the increasing level of endogenous gibberellins, especially in the apical part. This rising level appears as early as 7 days following blade division,i.e. at the time preceding the formation of marginal bud bases.
InBryophyllum crenatum plants the level of endogenous cytokinins was estimated in apical, middle and basal leaves, as well as in adjacent internodia. Maximum content was found out in the leaves from the middle stem part, which is probably associated with the capacity of this part to form marginal buds spontaneously also in intact plants. However, prior to flowering the maximum of cytokinin activity is shifted to the apical stem part.

The amounts of total phytol and its chlorophyll-bound and free portions have been determined quantitatively at different developmental stages of primary leaves of wheat using thin-layer chromatography combined with a potassium permanganate reaction. During the greening of etiolated leaves a close correlation exists between chlorophyll and phytol contents. Phytol is always present in excess and only in a bound state. During induced leaf senescence phytol is essentially degraded more slowly than chlorophyll. The liberated phytol does not influence the hydrolytic activity of chlorophyllase.

The effect of manganese chloride (10 mg Mn l^-1), EDTA (18 mg l^-1) and a mixture of these compounds on the nitrogen balance in maize xylem exudate was investigated. The compounds were applied as experimental solutions to the roots of 20 day old plants 24 h before excision. Application of Mn resulting in a lowered nitrogen level in the xylem exudate increased the relative content of the organic N-compounds in the exudate, particularly that of free amino acids. EDTA appreciably enhanced the content of total nitrogen in xylem exudate, however no significant changes were found in the proportion of inorganic and organic N-compounds in comparison with the water control. The significant features of the free amino acid exudate fraction of all experimental variants were, among others, the relatively high lysine content and the absence of proline arid sulphur containing amino acids. By gel filtration on Sephadex G-25 of xylem exudates UV (254 nm) absorbing fractions, four in the water control, five in Mn and six in EDTA variants were isolated. The UV absorbing fractions with the exception of one in each experimental variant (K_av 0.73 in water control, K_av 0.61 in Mn-variant, K_av 0.75 in EDTA and Mn + EDTA variant) were of peptide character, proline and sulphur-containing amino acids were missing in them. In the exceptional UV absorbing fractions (K_av 0.61-0.75) in spite of their high N-content (10.23%) after hydrolysis practically no amino acid could be detected.

Treflan has the ability to induce polyploidy inAllium cepa root tips. The frequency of polyploidy was reduced after allowing the roots to recover, which indicates that the process of polyploidy is a reversible one, if we apply Treflan for a short time (4 h). As soon as the chemioal is removed from the cells, they go on with their normal way in division. It was found that the concentration 350 × 10^-5 ml Treflan per 100 ml water is an effective concentration in producing polyploidy in the roots ofAllium cepa.
Treflan induced C-tumours in root tips ofAllium cepa. Two types of enlargement were noticed, complete swelling along the majority of root tips and complete swelling with a certain enlargement immediately after 2 mm terminal tips. The histological examination of these zones revealed that swellings were due to cell enlargement both in meristematic and in tumour zones. This conclusion was evidenced by the results obtained from the nucleoplasmic index.

The final length of the root cell is the result of a series of prooesses which represent a transition of the growing cell from its origin up to the completion of its elongation. These processes are associated on the one hand with cell proliferation, or, after the termination of proliferation, with the proceeding DNA synthesis, and with cell elongation on the other. The group of properties characterizing the growth region of the root as a cytologically heterogeneous complex, is at the same time the group of causes which affect the length of root cells. The individual cases documented in the paper point out the fact that the mechanisms regulating growth processes, have a locally limited action, often only within one single cell, and that they are simultaneously subordinated to the regulatory mechanism which controls the growth of the root as an entirety.

Calcium deficiency resulted in a 20% increase in the total content of phenolic compounds in the shoots of 10-day-old wheat plants and in a 10% decrease in the roots compared with the control. Differences in specific activities of the lyases of the shikimate pathway (L-phenylalanine ammonia-lyase, E.C.4.3.1.5, PAL; L-tyrosine ammonia-lyase, TAL) were established between control and Ca-deficient wheat and pumpkin plants. The lyase activities were higher in the shoots of Ca-deficient plants and lower in their roots, compared with the control. Thus, there is a certain correlation between PAL and TAL activities on the one hand and the content of phenolic compounds on the other. The time course of PAL activity during a few first days of growth and the dependence of TAL activity on pH were also investigated.

The distribution of endogenous gibberellin-like substances in individual organs ofZea mays L., cv. CE 250, plants was investigated during the transition from the vegetative to the generative phase of development. The gradient of the content of gibberellin-like substances and photosynthetic activity in leaf segments was followed in different parts of the Jeaves, as well as the changes in the content of gibberellin-like substances in leaf segments during an exposure in the light and in the dark. The gradient of the content of endogenous gibberellin-liko substances in the leaves, in the stem and in the spike is interpreted in terms of possible relationship of these compounds to the regulation of sink - source.

A field experiment was conducted to study the effects of N doses and row-direction on LAI, light transmission, plant height and dry matter production in the pure and mixed stands of 3 wheat (Triticum aestivum L.) cultivars Moti, Sonalika, and NP 824 differing in plant height. The mixed stands gave more transmitted light and shorter plants than the pure stands but dry matter production was not much affected. Nitrogen application increased the plant height, LAI, and dry matter but decreased the transmitted light. Row direction had no influence on plant height, LAI and dry matter production.

Following a previous biological and serological evidence of tobacco necrosis virus by means of an electron microscope, isometric virus particles of an average size of 26 ± 0.5 nm were found, in ultrathin sections prepared from the tissue of sprouting buds of underground stalks and from that of runners butts with symptoms of mosaic line pattern, as well as from the tissue of the indicator plantChenopodium quinoa.

Cucumber mosaic virus (CMV) isolates obtained from spontaneously infected (1)Chelidonium majus L. and (2)Impatiens parviflora DC. plants growing in the same part of a scree forest in central Bohemia showed differences in ten test plants, but not in further 26 plant species tested and in TIP. Slight quantitative differences between both isolates were obtained in serological tests. Properties of both isolates did not suit precisely any proposed CMV strain classification.

Paracytic, anisocytic, anomocytic, transitional forms, tetracytic, cyclocytic stomata and partly and completely amphicyclic forms are found, often on the same surface, in nine combinations. The most frequent type is paracytic. A few morphological variations in the basic types and eight types of abnormalities in stomata are recorded. The stomatal ontogeny may be mesogenous, mesoperigenous or perigenous. Trichomes are multicellular glandular club-shaped and unicellular eglandular. The taxonomic significance of stomata is indicated.

The effects of some growth regulators on the dark-germinating seeds ofCucumis anguria have been investigated. GA₃, 6-BA and ethrel strongly promoted the germination of seeds kept in white light. GA₃ had no effect in counteracting the far red effect, but did counteract partially the blue light. Ethrel partially counteracted both the far red and blue light effect. No interaction could be found between red light and GA₃ or 6-BA.

The activity of an enzyme system decomposing phloridzin was investigated in fruitbearing and nonbearing spurs of apple trees, Landsberger Reinette cv., throughout vegetation. Acetone powder obtained from xylem sap of apple spurs was incubated with phloridzinsubstratum in citric buffer at pH 5.5 for 12, 18 and 24 h at 30 °C. A paper and thin-layer chromatography as well aa a spectrophotometric assay were employed for tentative identification of enzymic degradation products. Phloretic acid (PA), co-factor of IAA-oxidase, as well as phloretin (Pin), and phloroglucinol (PI) were found after the digestion of phloridzin. The chromatographed enzyme reaction products were measured densitometrically. The activity of the enzyme system was estimated by its efficiency in PA production and phloridzin disappearance. Obtained values, expressed in percentages, showed that the enzyme activity in fruitbearing spurs was much higher than in nonbearing ones; 30 and 10% of released PA in July, respectively. Because fruitbearing spurs of the apple tree are possibly additionally supplied with auxin translocated from developing seeds, an adaptive character of the enzyme system producing PA, a known auxin repressor, is suggested.

Hydration level of seeds determines vigour of soybean,Glycine max (L.) Merr. The seeds should contain at least 20% of moisture for a good performance at low temperatures. This hydration level can be reached by pre-sowing exposure of seeds in water saturated atmosphere (WSA). The exposure decreases both visible symptoms of chilling injury and leaching electrolytes during imbibition, and increases both germination and growth of seedlings at 10 to 12 °C. It is concluded that the cell membrane integrity is re-established in a course of the WSA exposure.

The effect was studied of chloride ions, added in the form of different salts, on nitrate reductase (NR) level in excised pea roots, on anaerobic nitrite production in an assay medium lacking both nitrate and n-propanol, on nitrate content in the roots, and on in vivo NR activity determined in an assay medium containing 5% n-propanol. The presence of Cl in nitrate containing nutrient solutions resulted in lower NR levels, however counterions supplied together with Cl tended to modify slightly this general trend. The negative effect of Cl ions was also apparent, when Cl ions were applied before nitrate ions. Anaerobic nitrite production in the medium lacking both nitrate and n-propanol was not influenced by chloride ions. Nitrate content in the roots was reduced in the presence of chloride both at 3 mM and 15 mM NO₃ in nutrient solutions; however, at 16 mM NO₃, nitrate content in the roots exoeeded even in the presence of 15 mM Cl nitrate content in those root segments which were cultivated in a nutrient solution with 6 mM nitrate, which is the concentration at which NR reaches the level of saturation in excised pea roots. The results obtained suggest that a special induction nitrate pool exists in plant cells besides the storage and metabolic nitrate pools.

Isolated barley embryos were cultivated aseptically in three different complete media. The growth of the primary root of each embryo was measured during four days of cultivation. Embryos were cultivated on three different consistencies of media: on agar plates, on cellulose tissue moistened with the medium and in liquid shaken cultures. The last way of cultivation yielded the highest degree of the growth of roots. Optimum combination of conditions in shaken liquid medium was selected on the basis of systematic study. The growth of roots of isolated embryos under appropriate conditions approaches that of roots of seedlings cultived on moistened blotting paper.

Roots were excised from barley embryos cultivated in the complete liquid nutrient solution and cultivated in the same nutrient solution separately. The excised roots continued their growth but a progressive decrease in the growth rate was observed. There was a considerable short-term drop of the mitotic activity immediately after excision, which was followed by a compensatory increase and then equilibrium was reached 12 h after excision. During the next at least three days, the mitotic index of isolated barley roots varied between 5-6.5%, which is slightly lower than the mitotic index of the root meristems of isolated barley embryos under identical conditions. The mitotic cycle index of isolated barley roots and the size of the root meristem later decreased gradually.

Xylem exudates were collected from 20-day-old maize seedlings grown for 24 h in labelled manganese chloride solution (10 ppm) with or without EDTA (18 mgl^-1).
The distribution of radioactivity on paper ohromatograms of exudates did not show the existence of free Mn. Fractionation of exudate constituents by gel filtration on Sephadex G-26 showed that⁵⁴Mn is associated with three UV (254 nm) -absorbing fractions. Two fractions contain amino acids (M. wt.:≧ 10 000 and ∼ 900). The third fraction (M. wt. ∼ 600) however, appears to be a carrier of a different type, which is practically amino acid free, although it contains 10.23% N (by elementary analysis). The properties of this carrier are discussed. Application of EDTA has favoured the; transport of Mn in xylem sap with fractions of relatively lower molecular weights.

When cultivated in culture solutions salinized with different concentrations (0 to 100 meq I^-1), of either NaCl or Na₂SO₄, the oil producing castor bean, flax and sunflower plants exhibited significant changes in their water relationship parameters (stomatal frequency, rate of transpiration and water content). Although the trend of these changes was nearly the same, their magnitudes depended on the plant treated as well as on the type and level of the salinizing agent. In this respect the values of the stomatal frequency and the rates of transpiration increased significantly with the rise of salinization up to the level 40 meq I^-1. Above this the values of these parameters were generally reduced with the rise of salinization up to the highest level used. In addition a considerable number of stomata in either the lower or upper epidermis was found to be closed at the levels ranging from 60-100 meq l^-1. The water content of leaves of either castor bean or sunflower subjected to low or moderate salinization levels, remained more or less constant, but with a general tendency to decrease at high levels. However, in the case of flax the leaf water content was generally elevated at nearly all salinization levels.