Both nitrite reductase and nitrate reductase were induced by nitrite, but there were differences in the time course of induction and in the response to different NO₂^- concentrations between these enzymes. NH₄⁺ depressed the induction of nitrite reductase. NADH₂ dependent glutamate dehydrogenase activity was enhanced by those NO₂-concentrations in the medium at which unmetabolized NO₂^- occurred in the roots. NADPH₂ and NAD+ dependent GDh activities were not affected. In vivo modification and (or) in vivo activation were probably responsible for the increase in NADH₂ dependent GDH activity.

Peroxidase activity and isoenzyme pattern were investigated in buds and tubers of Jerusalem artichokes in relation to induction and breaking of dormancy. Peroxidase activity per unit soluble protein is the highest in the dormant stage. Conditions leading to growth,i.e. release of dormancy by the cold, stimulation of axial growth by gibberellic acid or stimulation of radial growth (tuberization) by kinetin, cause rapid loss of total peroxidase activity together with a decrease of intensity of the most cathodic isoperoxidases. Induction of dormancy by AMO-1618 increases peroxidase activity mainly through the same cathodic isoenzymes. The role of the cathodic isoperoxidases is discussed in relation to auxin catabolism and the genesis of oxygenation products inhibitory to plant growth.

Development of the shoot apex up to floral differentiation was investigated in the short-day plantChenopodium rubrum. The changes occurring in the apex from energence until full opening of the cotyledons (Figs 1-4), development during photoperiodic induction (Figs. 5-8), as well as the resulting floral differentiation (Figs. 9-10) are described. It was aimed at excluding the influence of plastochron changes on the interpretation of ontogeny of the shoot apex. For that reason two planes of longitudinal sections and two plastochron stages were compared.
In young plants zonation does not become fully evident prior to floral differentiation. The anatomical structure of the shoot apex does not change substantially during the first two inductive cycles which proved to be obligatory under the given experimental conditions. The changes occurring during two further inductive cycles correspond to the total activation of the meristems as manifested by the growth and branching of the apex preceeding floral differentiation proper.

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.

Exeised roots ofSolanum laciniatum Ait. grown in vitro in a liquid medium will form the typical rich white callus with a high water content. Its formation is made possible by the presence of 2,4-dichlorophenoxyacetic acid and niyo-inositol in the nutrient medium. Choline, ascorbic acid, riboflavin, calcium pantothenate and biotin are inactive. A mixture of thiamine, pyridoxine and nicotinic acid will induce only slight proliferation.

The nucleic acid fractions obtained by chromatography on MAK columns were compared in 4 variants ofChenopodium rubrum plants treated in different ways during floral induction. The first variant was normally induced to flowering. The second one was inhibited by application of FUDR to the apical bud on the third day of induction. In the third variant the inhibitory effect of FUDR was reversed by application of THY 24 h after FUDR treatment. In the fourth variant THY was applied 24 h after the termination of induction at a time when it was no longer able to reverse the inhibition of flowering. In plants treated with FUDR, a decrease in DNA and RNA synthesis was observed. After reversal of the inhibitory effect of FUDR by THY, DNA synthesis remained somewhat lower than in the control variant but RNA synthesis reached the same level as in the controls or even surpassed it. In plants to which THY was applied at a time when it was no longer possible to reverse flowering, the results obtained from different experiments were not identical. In some experiments nucleic acid synthesis remained lower than in the variant in which THY restituted flowering. In other experiments nucleic acid synthesis was fully restituted and reached the same level as in the control variant. This phenomenon is explained by the different size of the experimental plants at the beginning of the different experiments. The results are discussed with respect to the relation of the dynamics of nucleic acids to growth and development of the plants.

1. Kinetin at a supra-optimal dose of 1.0 mg/l reduces the growth inhibitory effect of CCC at 5 × 10^-2 M on tobacco callus and increases it on tobacco crown-gall.
2. CCC increases the content of total, acid soluble, protein anti nucleic acid nitrogm in both tissues. Kinetin partially reduces the effects of CCC on nitrogem metabolism in callus tissue, and increases it in crown-gall.
3. It is suggested that (1) CCC affects the synthesis of RNA directing the synthesis of protein, and (2) interaction of kinetin with CCC realizes via the genetic apparatus of the cell.

The influence of photoperiodic induction on the incorporation of uridine-³H into the shoot apices ofChenopodium rubrum was studied using the technique of autoradiography. No increase in uridine incorporation was detected either during induction lasting three days or immediately after its termination. Pyroninophylia likewise did not rise. However, changes in uridine incorporation related to morphogenetic activity during leaf formation and later during differentiation of inflorescences were well marked. The distribution of label in the nucleus immediately after three inductive cycles shows the ratio of extranucleolar to nucleolar incorporation to be higher in non-induced control plants than in induced ones.
Data from literature pointing to an activation of RNA synthesis during transition to flowering are discussed and compared with other systems where ontogenetic changes are accompanied by marked changes in RNA synthesis. It is assumed that the activation of RNA synthesis after induction is connected mainly with the activation of growth. However, inChenopodium rubrum photoperiodic induction proceeds together with limited growth and without activation of RNA synthesis.

Whole seeds, excised embryos, and excised endosperm ofSantalum album were aseptically cultured with a view to studying seed germination in isolation from the host species, and to establishing callus cultures from both embryo and endosperm for comparative studies et their morphogenesis. Seed germination and seedling formation occurred normally only on modified White's medium supplemented with casein hydrolysate or coconut milk, or with both substances. Neither the excised embryo nor the endosperm grew on any of the culture media tested. However in about 17 per cent seed cultures on White's medium supplemented with 2,4-D, kinetin, and yeast extract, the endosperm degenerated, whereas the embryo callused and subsequently differentiated into innumerable embryoids; eventually the embryoids developed into normal plantlets. Callusing of the endosperm occurred also in seed cultures on four media supplemented variously with 2,4-D, kinetin, and yeast extract. Although the endosperm tissue grew through several passages no organ fornation was observed.

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.

CCC (2-chloroethyl)trimethylammonium chloride applied to plants ofChenopodium rubrum during floral induction led to an increase in the level of endogenous cytokinins in the apical buds. Application of gibberellic acid or indole-3-acetic acid at concentrations reversing the effect of CCC reduced the level of cytokinins. After simultaneous treatment with both CCC and one of the growth substances this reduction was less pronounced. From the comparison bf the present results, as well as of those published in previous papers it follows that in apical buds ofChenopodium rubrum there exists a mutual interaction between gibberellins and cytokinins. Under certain conditions both these groups of hormones may substitute for each other in flowering. IAA seems to affect flowering by regulating the level of both gibberellins and cytokinins.

Floral buds ofBrowallia demissa, at three stages of development, were cultured on Nitsch and Nitsch basal medium. The supplements used include IAA; several cytokinins- benzyladenine, kinetin and 6-benzyl-9 tetrahydropyran-adenine (SD 8339); gibberellic acid (GA₃); 2, 3, 5-triiodobenzoic acid (TIBA); arginine and cysteine. All three stages of floral buds failed to complete development. In some treatments stages II and III produced callus and/or roots from the morphological basal end. Cytokinins promoted bud formation whereas both IAA and GA₃ depressed bud formation The shoots differentiatedin vitro were capable of setting flowers, fruits and seeds in all the treatments. The seeds were viable. Comparative studies of development of flowersin vivo andin vitro were made. In some treatments the flowers exhibited abnormal corolla, and roecium and gynoecium. Factors affecting normal bud initiation, organization and development are discussed.

Flower initiation induced by three inductive photoperiods inChenopodium rubrum L. was fully inhibited by treating the shoot apex with a 5 μl drop of 1×10^-5 m 5-fluorodeoxyuridine (FDU). This inhibition may be reversed by thymidine applied simultaneously with or after FDU treatment at any time during photoperiodic induction. One day after the end of induction the inhibition caused by FDU is irreparable even by increasing thymidine concentrations. It is concluded that photoperiodic floral induction may take place inChenopodium even if DNA synthesis is suppressed.

On incubation of the callus tissue ofDaucus carota L. in solutions of glucose-6-¹⁴C and -1-¹⁴C the distribution of radioactivity in the molecule of endogenous glucose will change and the ratio of activities of liberated¹⁴CO₂ (C₆/C₁) will rise The limits of possible changes of specific activity of¹⁴CO₂ and of the C₆/C₁ ratio were calculated with respect to the observed randomization and it was shown that the mutual exchange of carbon atoms in the molecules is not the decisive cause of the rise of the ratio.
The specific radioactivity of¹⁴C in CO₂ is as much as 12 times higher than that of endogenous glucose and fructose and about twice as high as the theoretical maximum. This might indicate that in addition to the cytoplasmic fraction of glucose the callus cells contain a fraction of low metabolic activity, most likely in the vacuoles, that could account for some of the increase of the C₆/C₁ value.
The main reason for the changes in the C₆/C₁ ratio is envisaged in the establishment of isotopic equilibrium between the pentose cycle and glycolysis and other metabolic systems, in particular via triose phosphates, the radioactivity of which can greatly affect the C₆/C₁ ratio, as was shown in a model experiment.

The application of CCC at concentrations inhibiting flowering ofChenopodium rubrum reduces the level of endogenous gibberellins in the apical buds of the plants. The effect of CCC may be reversed by appropriate concentrations of gibberellin (GA-), indole acetic acid (IAA) or kinetin. Kinetin applied to the apical bud during floral induction reduced the level of endogenous gibberellins similarly as CCC and if both CCC and kinetin were applied simultaneously their action was additive. On the other hand IAA applied under the same conditions increased the level of endogenous gibberellins and after joint application of CCC and IAA their level was the same as in untreated control plants. After application of CCC during floral induction the level of endogenous auxins did not change markedly but an active substance "x" appeared on the chromatograms of indole compounds. This substance was found also after simultaneous application of GA- and CCC but not after joint application of CCC and kinetin. If follows from our results that the same morphological phenomenon (flowering) can take place in plants considerably differing as to their level of endogenous growth substances. The ratio of different growth substances is obviously more important than the actual level of the single substances.

The induced meiotic abnormalities as a result of sprayingVicia faba plants with aqueous saturated solutions of podophyllin and 8-hydroxyquinoline were studied. The 2 drugs induced the same types of abnormalities including lagging chromosomes, stickiness, and bridges. The main difference between the 2 agents was the induction of polyploid P.M.Cs. by 8-hydroxyquinoline.

Floral differentiation ofChenopodium rubrum is more AD-sensitive than growth of the vegetative organs. With a suitable combination of the manner of application and the concentration of AD used, selective inhibition of flowering can be attained without any effect on growth. The inhibition of flowering was greatest if AD acted during the first two days of photoperiodic induction. With later application its effect on flowering was weaker. RNA synthesized in the first days of photoperiodic induction to a considerable extent ensured its further course.

The effect of 2-thiouracil on vegetative growth and floral differentiation was investigated inChenopodium rubrum plants grown in water cultures. Between the low concentrations of the agent, stimulating vegetative growth and floral differentiation, and those inhibiting both these processes, a narrow concentration range was found (1.10^-5 m to 2.10^-5 m), where growth was inhibited selectively. At a concentration of 1.10^-4 m a selective inhibition of development was found when 2-thiouracil was applied at the beginning of photoperiodic induction. Inhibition of development was strong regardless of whether 2-thiouracil was applied before, during or closely after 4 days of photoperiodic induction; the degree of growth inhibition, however, changed in dependence on photoperiodic induction. The strongest relative inhibition of development, calculated as a ratio between development and growth, was observed always at the beginning of photoperiodic induction.
Investigation of plant growth as well as the anatomical and autoradiographic study after the application of 2-thiouracil indicate that the inhibition becomes evident at the end of 4 days of application by an overall growth inhibition and a decrease of mitotic activity. Reversal by uracil was possible after simultaneous application of 2-thiouracil. The nature of the selective inhibition is discussed and two possible interpretations of the data obtained are analyzed: a) different response of growth processes in apices and young vegetative organs respectively with regard to different participation of cell division and elongation, b) specific inhibition of floral differentiation.

The callus tissue derived from tobacco pith and subcultured for 5^1/2 years on a solid synthetic modium revealed considerable differences in cell division activity depending on the age of the subculture and diurnal rhythm. The callus cells exhibited different level of ploidy among which an aneuploid condition nearer to diploid (2n=30-50) predominated. Chromosomal bridges and other structural rearrangements (lagging chromosomes, fragments) were observed in ana-and telophase.

The effects of low doses of two mutagens (UV-light and ethyl methansulphonate) on the growth of algae on a solid minimal (anorganic) medium were studied. It was supposed that low doses of mutagens will be more suitable for the induction of growth mutations.
The UV-light had an inhibitory effect in the whole range of the applied doses on the growth of colonies of algae from the cells inoculated on the solid medium immediately after irradiation.
Ethyl methansulphonate produced growth stimulation if applied in the lowest doses. The growth was inhibited in a further range of doses and then there appeared the range of lethal doses.
The growth responses to the influence of these mutagens were different in all the three algal species used and to the previous cultivation conditions before their exposure to the mutagens. It is certain that most of these growth responses are only modifications.
The influence of ethyl methansulphonate differed according to the method of application. If it affected the algae for a long time (it means if they were inoculated directly on the solid medium containing mutagens), or, if the algae were exposed to its influence immediately before their inoculation on the solid medium, the growth responses of colonies were quite different.
Growth responses with the single studied strains differed quantitatively only.

6-azauracil (AU) and 2-thiouracil (TU) were applied to the short-day plants Pharbitis Nil and Chenopodium rubrum and to the long-day plants Hyoscyamus niger, Lolium temulentum and Triticum aestivum cv. Chlumecká 12 at different times before, during or at the end of floral induction. In wheat the effect of 5-bromouracil, 5-iodouracil and 2-thio-6-azauracil was also tested.With the exception of bromouracil, which slightly stimulated flowering in wheat, all analogues either strongly inhibited or completely blocked flowering when applied in appropriate concentrations a short time prior to induction or at its beginning. Treatments given a longer time before induction or after its termination was less effective. Inhibition of flowering was always associated with damage to the vegetative growth. The effect of TU was reversed by uracil and that of AU by uridine, if these compounds were applied simultaneously with the analogue at a concentration exceeding at least 5 times that of the analogue. Reversal also applied to vegetative growth. Simultaneous application of gibberellin and analogues did not remove the inhibition.

In the basal growth medium only the ovaries excised 15 days after pollination reached maturity. In a medium containing IAA (5ppm) and kinetin (0.5ppm) ovaries excised even 10 days after polliration produced viable seeds.
Young ovaries formed in the pedicel region a callus, which later differentiated into roots; older ovaries (excised 15 days after pollination) produced callus tissue and roots from the ovary wall.

1. Teucrium Scorodonia L., plante vivace et caulescente, doit être placèe à 3°C pendant 8 semaines au moins, pour être vernalisé.
L'induction et l'initiation florales ont lieu en jours longs.
2. Chez cette plante, l'état vernalisé est instable dans les bourgeons axillaires ainsi que dans le bourgeon terminal qui peut être dévernalisé, même après une réfrigération complètement vernalisante, par des photopériodes courtes ou par des températures élevées (35°C).
D'autre part, la dévernalisation des bourgeons axillaires consécutive à l'inhibition de la croissance de ces bourgeons par la dominance apicale, est un mécanisme naturel assurant la pérennité de la plante.

A study was made of the anatomical structure of the shoot apices ofHyoscyamus niger L. in plants which were transferred from a long-day to a short-day regime after the initiation of the inflorescence. After a certain time these plants are reverted to the vegetative stage with the inhibition of the development of further flower buds and the renewed production of rosette leaves. The inflorescence apex consisted of a few superficial layers of cells and a corpus composed of slightly elongated cells. The anatomical structure of the apices which were reverted into the vegetative state resembled that of shoot apices in the intermediate stage. The apex had several layers of small cells, under which there was a group of small but irregularly arranged cells which passed into the rib meristem.
The shoot apices of plants transferred from a long to a short-day regime at different time intervals after fulfilling the requirements of minimal photoperiodic induction thus, on the short day, display morphological and anatomical characteristics of various degrees of transition from generative to vegetative stage.

Proliferation of the cambium and parenchyma of branches from 34 tree species was studied by means of tissue culturesin vitro. The formation of callus tissue, the seasonal activity of cambium, the effects of indole-3-acetic acid on the reactivation of cambium and the polarity of callus formation were investigated.
Various tree species are characterized by a different capacity for callus formation; in the majority of species, however, the reaction of cambium takes place in culturesin vitro. Some species produce callus from the cortex and the pith of branches and the lenticels simultaneously with the reactivation of cambium.
Growth of callus tissue was maximal in winter, adequate in spring before budding occurred and later decreased greatly. During the summer the growth-rates increased again and in the autumn were close to those encountered during the winter. Some species are characterized by a similarly intensive cambial proliferation throughout the whole year.
Indole-3-acetic acid (IAA) in the cultivation medium had various effects on the growth of callus tissue in the species examined. A series of species initiated meristematic foci in callus tissues that gave rise to roots (more frequently on media with added IAA) or to buds and stems.
The position of the sections in the medium (whether the apical end was placed upwards or downwards) had no great effect on the polarity of callus formation. Some species produced callus tissue at both ends of sections.

From photoperiodic experiments and an anatomic study of the shoot apex in the facultative short-day plantsPerilla ocimoides L. it was shown in all cases that gibberellic acid (GA) application did not accelerate flower induction. Between the development grades 2 and 4, GA caused a certain temporary acceleration which, however, completely equalised in a short period and plants of both variants SD and SD+GA flowered at the same time. Long day plants (LDand LD+GA) also flowered simultaneously with a certain delay. GA caused the total length of the plant to increase in both cases by more than a double, while preserving practically the same number of leaf pairs in variants under the same photoperiodic regime.

The paper describes a new strain of tobacco mosaic virus which has been named S-strain of TMV because of its characteristic stripe symptoms. The Al-strain of tobacco mosaic virus was used as the initial material.
In contrast to methods used hitherto the S-strain was obtained by interfering with the metabolism of the host plant by a change in the environment. (SvobodovÁ 1954, 1958). The usual hosts of tobacco mosaic virus were used, chiefly tobacco and tomato plants. These plants were cultivated under aseptic conditions on an agar medium in Erlenmeyer flasks with a reduced amount of nutrients, a shortened period of illumination and a limited air supply, so that they were stunted. Following the passage of the initial Al-strain of TMV through these dwarfed plants changes in symptoms appeared, which became apparent only after further passages through plants grown under normal conditions in a glass house in garden soil, where the virus once again had normal conditions for reproduction. Of the new symptoms obtained, only the most striking were further studied (the symptoms of S-strain). By means of alternating of the passage of the Al-strain of TMV from normal-to dwarfed-to normal plants grown under artificial nutrient conditions, i. e. a twice or thrice repeated sudden change of environment, the new strain (S-strain) was obtained five times in all and at different times of the year. From the symptomatic point of view no differences were found in the different repetitions of this change. The results were also the same for material from tomato plants and from tobacco of the Samsun variety.
The origin of the new strain was not caused only by the stuntedness of the host plants. It was also necessary to influence its metabolism by an abnormal environment (particularly insufficient air) in the Erlenmeyer flask before and after inoculation.
Following the reverse passage of the S-strain from plants grown normally in a glass house to dwarfed plants in an artificial environment no further changes occurred. Neither did the passage to ten other hosts grown normally on garden soil and in artificial nutrient produce any further change in symptoms. The S-strain has been maintained by a succession of continuous passages throughNicotiana tabacum Samsun for six years, and each year mass inoculation of a large number of plants is carried out. We therefore now consider the change to be permanent.
Indirect influencing of the virus through a change in the metabolism of the host plant sufficed for the induction of the new strain. Its symptoms appeared only after passage through normal unaffected plants, where the virus reproduction was not inhibited by the retarded growth of the host plant. There is a certain similarity in the emergence of the S-strain and the TM44-stram, obtained byPfanchuch et al., with X-ray irradiation. However, the initial material was the ordinary green strain of TMV.
The biological, chemical and other characteristics ascertained for S-strain and a comparison of these with the characteristics of the initial Al-strain and the ordinary green strain of TMV will be published later.