The presence of beet yellows virus (BYV) particles was electron microscopically proved in the roots of sugar beet. Specimens for the electron microscopical examination of root sap were prepared by differential centrifugation. It was proved that, contrary to expectations, examinations in spring showed most virus particles in the basal part of the root. At the same time it was found by experiment that the diagnostical BYV antiserum, for which the antigen was prepared from sugar beet leaves, did not react with a purificate of BYV containing virus particles.

A purified potato virus S was prepared using precipitation by the solution of 35% polyethylene glycol 4000 in the presence of an electrolyte. The mixture for precipitation of the potato virus S had to contain 11% polyethylene glycol and 0.25m NaCl. The S virus was extracted by 0.01m phosphate buffer, pH 7.5, from the precipitation separated by centrifugation. One part of the extract was further purified by means of differential centrifugation and the other by means of gel filtration on Sephadex G-100. The ultraviolet absorption measurements of both preparations showed that the differential centrifugation gave a purer preparation than the gel filtration.

2,4-D was applied to the roots of diploid and tetraploid corn. After the application the mitotic division in the meristem of root tips was blocked; the mitotic division in differentiated cells of cortex and central cylinder, on the other hand, was provoked. In the cortex of diploid corn (variety České) predominantly tetraploid were found cells with 28 chromosomes and, to a lesser extent, octoploid and diploid ones with 56 and 14 chromosomes respectively. In the cortex of tetraploid corn (variety Bernburger Tetraroggen), most cells were octoploid with 56 chromosomes; the metaphase levels with 112 and 28 chromosomes, e.g. 16-ploid and tetraploid cells, were found less frequently. The relations between the numbers of cells with different polyploidy were similar in both the varieties. The first endoreduplication cycle was different polyploidy were similar in both the varieties. The first endoreduplication cycle was found to occur in the region where the cortex cells finish their elongation. In the central cylinder of the roots of diploid corn most cells were found to be diploid, in tetraploid corn most cells were tetraploid.

The production of pectic enzymes byHelminthosporium atypicum and its morphogenesis on different media were studied. It was observed that the fungus produces pectic enzyme (macerating enzyme) adaptively. Increasing concentrations of glucose had an inhibitory effect on enzyme production. Glucose promotes profuse growth and early sporulation whereas presence of pectin slows down the growth and delays sporulation. Delay in sporulation is the effect of presence of pectin and not of the low pH of the medium. It is also suggested that in the case ofH. atypicum low pH of the medium does not allow the fungus to utilize a carbon source as efficiently as at higher pH.

Versuche, in denen der Einfluss der Phenäthylpyridine (I A, B, C), trans-Styrylpyridine (II A, B, C) und Pyridylphenylazetylene (III A, B, C) auf die Aktivität der Pyrogallolund der Ascorbinsäure-Oxydase in den Wurzeln vonSinapis alba-Keimlingen verfolgt wurde, ergaben folgende Resultate:in vivo wurde die Pyrogallol-Oxydase durch keinen dieser Stoffe beeinflusst, jedochin vitro zeigten die trans-Styrylpyridine und die Pyridylphenylazetylene eine bedeutende Hemmung. Die gefundenen Resultate lassen darauf schliessen, dass es sich wahrscheinlich um eine direkte Inhibition, diein vivo durch Einschaltung dieser Stoffe in den Stoffwechsel teilweise kompensiert wird, handelt. Die Aktivität der Ascorbinsäure-Oxydase war dagegen mächtig gesteigert, besonders in den Versuchenin vivo.

The work described here was carried out during the last three years mainly on the castle premises at Lužany near Přeštice (Hlávka's foundation). It dealt with the disease of the horse chestnut-tree (Aesculus hippocastanum L.). The symptoms and their development have also been observed at a number of other places. According to the classification ofBose (Wageningen) the symptoms belong to the groups of Colour changes (II), Necrosis (IV), Deformation (VII) and partly also Growth reduction (of fruits). We are dealing here with a disease that was described bySorauer andThomas 60 years ago as abiosis. Since some of the symptoms suggested a virus origin of the disease some diagnostic tests were carried out. The serological test was negative on account of the chemical composition of chestnut leaves which are not amenable to such tests. Grafting and inoculating tests on healthy seedlings were positive. Viral necrosis of the horse chestnut is a disease of the system which is not transferred by contact. It is readily transferred by grafting and inoculating. Some symptoms suggest that it can also partly be transferred by seeds.

Obwohl auf Grund vieler Untersuchungen vermutet werden konnte, daß die sog. Kakteen-Eiweißspindeln, d. h. die ZelleinschlÜsse des Kakteen-X-Virus (CaXV), aus zahlreichen verlängerten Partikeln des OaXV zusammengesetzt sind, war das dennoch bis jetzt noch nicht bewiesen. Deshalb versuchten wir im Laufe dieser Untersuchungen mittels der fluoreszierenden Antikörper festzustellen, ob die Eiweißspindeln wirklich Aggregate von Viruspartikeln darstellen.
Bei dieser Untersuchung wurde die sog. indirekte Methode angewandt. Dabei haben wir zuerst die spindelhaltigen Zellen mit dem durch Immunisierung der Kaninchen hergestellten homologen Serum gegen CaXV behandelt, und erst nachher dieselben Zellen in eine Lösung von fluoreszierenden Antikörpern gegen das Kaninohen-γ-Globulin eingelegt. Nach dieser Behandlung leuchteten die Eiweißspindeln im Fluoreszenzmikroskop kräftig gelbrÜn (Fluoresce-inisiothiocyanat). Diese Fluoreszenz bewies uns, daß die positive Reaktion eingetreten ist und daß die Eiweißspindeln aus Viruspartikeln aufgebaut sind. Mehrere Kontrollversuche haben die Genauigkeit unserer Grundversuche bestätigt.

The activity of 1-methyl-1-nitrosourea (MNH), 1-ethyl-1-nitrosourea (ENH), 1-methyl-3-nitro-1-nitrosoguanidine (MNG) and 1-ethyl-3-nitro-1-nitrosoguanidine (ENG) was tested on seeds of barley andArabidopsis. The activity of nitrosoamides tested was expressed by the germination and M₁ seedling height reduction of barley and M₁ root length reduction ofArabidopsis.
1) After the action of both nitrosoureas (MNH and ENH) the germination of barley is at the same level as that of controls, even at concentrations, leading to a maximal reduction in the height of seedlings. After the action of both nitrosoguanidines (MNG and ENG) germination decreases in parallel with the decreasing seedling height. InArabidopsis no such differences in the relation germination to root length reduction were observed after nitrosoureas and nitrosoguanidines treatment. The differences in the M₁ generation of barley andArabidopsis after nitrosoguanidines treatment may be the reason for the non-mutagenic action of MNG and ENG in barley.
2) All 4 tested nitrosoamides are active between pH 3 and pH 6 and almost entirely ineffective at pH 7 and in basic solutions.
3) The effectiveness (in relation to M₁ seedling height reduction) of the tested nitrosoamides with a methyl group (MNG and MNH) is higher than of the nitrosoamides with an ethyl group (ENG and ENH).
4) 50% decomposition of aqueous solutions (at 25° C) of MNH and ENH takes about 60 hours, for MNG 120 hours and for ENG 420 hours.
5) Aeration during treatment or a period in the cold (5° C) after treatment improved the germination of MNG treated seeds. Sucrose, KNO₃ and thiourea had no effect.

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 enzymatic transamination reactions between aspartic and α-ketoglutaric acid and between aspartic and pyruvic acid were studied in fresh dialysed extracts of young wheat plants cultivated under various trophical conditions, in mineral solution (Knop), in the solution of an soil organic substance (potassium humate) and without nutrients (H₂O). Simultaneously, the level of endogenic aspartic acid, glutamic acid and the growth values were determined. The enzymatic reactions were characterized by determining the optimum pH, the time course, and the effect of coenzyme and of inhibitors.
The activity of the aspartate-glutamate transaminase from the root system of plants was considerably higher than the activity of the overground organs. The enzymatic activity from both parts of the plant was inversely proportional to the growth rate: intensive growth of the plants from the Knop variant was connected with their low enzymatic activity; the level of endogenic glutamic acid was high. The slow growth of the plants without nutrients was connected with a higher enzymatic activity; the level of endogenic glutamic acid was low. The plants from the potassium humate variant had an intermediate position between these two variants from the point of view of growth as well as from that of enzymatic activity. The plants with insufficient nutrition (slow growth, low level of endogenic glutamic acid) apparently have a low capacity for supplementing the glutamic acid deficit, which is essential for the metabolic processes, by increasing the activity of the reactions leading to glutamic acid synthesis (Asp-Glu) and, on the other hand, by decreasing the reactions utilizing it (Glu-Ala). For wheat plants the active aspartate-glutamate reaction is obviously physiologically more important than the direct reaction glutamate-aspartate and the reaction aspartate-alanine which in all cases had a very low activity.

U odr. Blenheimská reneta se postřiky α-naftyloctové kyseliny na letorosty strormů bez plodů neprojevily vyšším počtem založených květních pupenů. Autor proto dospěl k názoru, že otázka přímého zapojení a přímého vlivu α-naftyloctové kyseliny na zakládání kvétních pupenů u jabloné je sporná.

Cinematographic records of longitudinal growth showed that hypocotyl with radicle inPisum sativum L. undergoes spiral oscillations during growth. This phenomenon can be characterized by the following time-space limits:
(1) Curvature of the hypocotyl with radicle takes place always in the zone of most rapid elongation (Fig. 2, 8).
(2) Maximum deflections of the root tip from a straight positive geotropic direction of growth correspond to the time when the maximum growth rates were demonstrated (Table 4, Fig. 8).
(3) Shift of zones of maximum elongation proceeds in a spiral path, acropetally to the region of the root tip; as may be seen from the results obtained by studying the growth of roots of perennial (woody) plants this mechanism is preserved throughout ontogeny (Head 1965).
When studying these self-regulating mechanisms the author suggests to use the principles valid for control systems with feedback as a mechanism eliminating errors.

A method of calculation for determining the total transpiration (consumption of water for transpiration) of a single woody plant seedling or of their growth during periods of different length (from one day up to the whole vegetative season) is described and critically evaluated; the calculation is performed according to single transpiration intensity measuring results, by the cut-shoot method and weighing at 8, 11, 14 and 17 hours (or more often during the day).

Measurements of the size of the nuclei of dioecious plants showed that the nuclei of male and female plants differ in agreement with the larger quantity of chromatin. The male. plants ofRumex acetosella andMelandrium album had larger nuclei, their Y chromosome being larger than the X chromosome, the same is true forRumex acetosa where the Y chromosome is smaller but there are two in the set.Ginkgo biloba had larger female nuclei because the Y chromosome was smaller than the X. The curves obtained by grouping all the nuclei of both sexes never had two peaks with regard to the small differences between the classes of maximum frequency.

The paper deals with the study of morphological differentiation of flower buds in 10 varieties of apple-trees in relation to the growth of summer shoots and the earliness of varieties. The data obtained indicate that in the warmer regions of Slovakia the critical season of transformation of flower buds from vegetative to generative forms takes place, on the average, between July 20 and 29, and, at the same time, the variety Yellow Transparent deviates from the average four week-earlier. According to the author we can speak neither of a positive relation between the onset of morphological differentiation and the active growth of summer shoots nor of the relation between the earliness of the variety in maturing and the onset of differentiation. The morphological differentiation may be classified into five phases: 1^st phase - the formation of the growing point primordium, 2^nd phase - the formation of the cup on sepal primordia, 3^rd phase - the formation of petal primordium, 4^th phase - the formation of carpel and stamen primordia, 6^th phase - completion of the differentiation through substantial enlargement of flower organs before the onset of winter.

Par la température de ľunique journée longue permettant la mise à fleurs chezAnagallis arvensis, il est possible do déterminer la formation do 2 types do boutons, par la suite, en jours courts: les uns évoluent en fleurs normales; les autres on fleurs proliféres - mais dans tune proportion do 50% seulement. Excisés précocement, à un stade de leur dévoloppement oè seuls, les sépales sont initiés, ces 2 types de boutons sont placésin vitro sur un milieu simple. Leur développement s'achéve, sur ce milieu, par la formation, soit de fleurs normales s'épanouissant, soit de fleurs proliféres dans la mêm proportion quein vivo. Ces résultats sont discutés dans le cadre du schéma proposé par Heslop-Harrison comme hypothése ďinterprétation de ľorganogenése florale.

The paper deals with the relationship between the glucose utilization and growth ofPenicillium frequentans. The vegetative growth was scanty and sporulation started at a time when glucose was abundant in the culture medium. Occurrence of autolysis in spite of the presence of glucose in the culture medium is a peculiar phenomenon reported here. The autolysing culture gives rise to conditions which favour the germination of spores and the development of vegetative growth. The citric acid is the major metabolite produced by the fungus and its biochemical origin appears to follow condensation of oxalacetate and acetate. Lastly production of citrmin as another metabolite has also been reported.

It has been established that mannitol infiltrated in a vacuum into plant tissues increased the oxygen uptake. No lag phase appearing subsequently to its infiltration by the transpiration stream (Trip, Nelson, Keotkov 1963) was observed. Our results may support the opinion that the mentioned lag phase is caused by the slow penetration of mannitol into the plant cells.

Kinetin (10^-4 m) is initially more effective than GA (10^-4M) in reversal of the inhibitory effect of Phosfon D (10^-3m) on the germination of kale seed (Fig. 2 and Fig. 3). Kinetin is about 2.5 times more effective than GA in reversal of the synergistic inhibitory effect of coumatin (100 p.p.m.) plus Phosfon D on germination of kale (Fig. 2 and Fig. 4); initially most effective in this respect is a supraoptimal concentration of kinetin, 5 x 10^-4M, which markedly inhibits germination in the control.
It seems that kinetin, Phosphon D and coumarin act specifically on the process of germination. It is suggested that in the germinating seed of kale Phosfon D and coumarin block alternative metabolic pathways, induced by kinetin.

V popsaných pokusech byl vliv letního odlistování na zakládání květních pupenů do značné míry závislý na odrůdě a byl silnější u stromů vykazujíeích bujnější růst.

When the lethal radiomutant chlorina 42 was cultivated on glucose containing and glucose-free medium the cotyledons of the matant sown on glucose medium had a higher chlorophyll content than those of the matant sown on glucose-free madium. In further cultivation of this mitant on glucose medium until flowering the total chlorophyll content is maintained at the same level, it increases slightly in the case of flowering plants. The mutant cultivated on glucose medium differs somewhat with regard to the content of free amino acids from the green control cultivated also on glucose medium over the whole vegetation period. The former has a higher glutamine content than the latter and in some growth phases also a higher content of asparagine. It is assumed that the insufficient photosynthetic activity is apparently not fully compensated by glucose and the plant has to supplement its energy balance by partial oxidative protein catabolism even under the conditions of artificial nutrition.

When compared with the control plants, the increase in dry weight in the growing parts of germinating plants ofPisum sativum L., cultivated in a closed atmosphere in darkness or light is heavily inhibited. The concentration of carbon dioxide in the closed atmosphere increased in 60 mg CO₂/per 1 g of the final dry weight of plants after 10 days. Similar results were obtained with older plants under similar conditions. The Knop solution caused a slight increase of dry weight in the growing parts of plants, but did not change considerably the relations in gas exchange. The results show that even plants which are able to photosynthetize, are only transpiring under the above conditions; first, when the plants were devoid of cotyledons, as storage organs, the changes in their dry weight (but not the changes in the CO₂ and O₂ exchange in a closed atmosphere) seemed to show photosynthetic income of CO₂ (while its concentration increased to 3-6 volume %) when compared with the control.
From the above results follows that quantative relations between photosynthesis respiration cannot be solved by analysing the gas exchange in a closed atmosphere.

Identification trials were carried out to determine a virus-like disease of Impatiene parviflora DC. Two forms of foliar symptoms were observed:
a) Chiorotie and necrotic areas sometimes fallen out, leaving the leaves "shot holed";
b) milder foliar symptoms consisting of slight greenish yellow areas and spots often scarcely visible except by transmitted light.
Results of experiments with the first form of the disease demonstrate the identity of the causal virus with cabbage black ringspot virus; the second type of symptoms was caused by a Strain of cucumber mosaic virus inducing unusual symptoms in tobacco plants.

In der Arbeit wurde die Möglichkeit der allelopathischen Beeinflussung von Folgepflanzen durch Vorkulturen bei der Kultivierung in abgestuften Zeitintervallen nacheinander auf demselben Bodensubstrat bei folgenden Konabinationen von Pflanzen untersucht: Mohn - ZuckerrÜbe, Ackersenf - Gerste, Hanf - Korn, Zwiebel - Raps. Die Versuche wurden in Gefassen mit Komposterde, welche im Laufe des Versuches im Garten in den Boden eingelassen worden waren, durchgefÜhrt. Es wurde das Wachstum der Vorkulturen und der Folgepflanzen in den ersten Wachstumsphasen untersucht. Von der Aussaat der Folgepflanzen wurde in Bodenproben die Respirationsintensität, die aktuelle Feuchtigkeit und der Gehalt an physiologisch zugänglichem Stickstoff, Phosphor und Kalium bestimmt.
In allen untersuchten Kombinationen waren die Folgepflanzen durch die Kultivierung der Vorkultur und die nachfolgende Lagerung des Bodensubstrates beeinflusst. Die Wachstumsveränderungen der Folgepflanzen standen teilweise mit dem Gehalt an physiologisch zugänglichem Stickstoff im Bodensubstrat in Korrelation. Aus dem Charakter der Wachstumsveränderungen ging jedoch auch klar hervor, dass sich hier auch allelopathische Faktoren beteiligt haben. Sehr inhibierend wirkte Mohn auf ZuckerrÜbe, weniger inhibierend wirkte Ackersenf auf Gerste und Zwiebel auf Raps. Die Wirkung von Hanf auf Korn zeigte mit der Lagerungsdauer des Bodensubstrates zusammenhängende Veränderungen.
Veränderungen im Gehalt an physiologisch zugänglichem Stickstoff, Phosphor und Kalium im Versuchsbodensubstrat entsprachen nicht der Menge der angewachsenen Pflanzenmasse der Vorkultur, was durch die angewendete Kultivierungsmethode bedingt war. Die verhältnismässig schnelle Erneuerung der durch die Vorkultur erschöpften Nitrate im Versuchsbodensubstrat in der Zeit der Bodenlagerung wurde wahrscheinlich durch Nitrifikationsprozesse verursacht.
Den festgestellten Veränderungen der Respirationsintensität des Versuchsbodensubstrates nach kann sich auch die Bodenmikroflora an der allelopathischen Beinflussung beteiligen.

1. A number of varieties of cultivated juteGorchorus oHtorius L. andG. capsularis L. were tested in artificially created drought, waterlogging and control conditions.
2. The number of lateral roots with secondary growth was reduced to the minimum inC. capsularis under waterlogged conditions, but the weight of the roots was increased to the maximum, due to the production of numerous spongy and fibrous roots.C. olitorius suffered in both the characters under similar environment and failed to produce fibrous and spongy root. This species gained in root weight and lateral root number in drought under whichC. capsularis suffered in these two characters. These were the main features of adaptation of these two species.
3. Within species among varieties the variations regarding these two characters have been found to be controlled by genotypes. Lateral root number within both the species has been found to be a more strongly heritable character than root weight. Expected genetic advance has revealed the scope of selection for lateral root number.
4. While variations among thé varieties within species have been interpreted as an expression of phenotypic flexibility, the variation between species is an expression of phenotypic plasticity, which is an outcome of basically physiological mechanisms.Corchorus capsularis L. andC. olitorius L. are two cultivated jute species. The most striking distinction between these two species hitherto known is that whileG. capsularis can withstand waterlogging successfully,C. olitorius cannot. This general view formed the basis of testing these species under artificially created environmental stresses to find out the general components contributing to this specific difference.

The redox potential of wilted leaves of cereal seedlings grown in a greenhouse was higher than in the fresh leaves. However, the redox potential in the wilted leaves of plants during the stem extension was lower than in fresh leaves. The reaction of barley leaves var. Japan 2003, which belongs to the dundar-beyi Zhuk.-group, differed materially from the European cereal varieties. The cause of the change of redox potential is discussed in connection with the ontogeny of cereals and resistance against obligate parasites.

Root formation in the etiolated pea stem sections and inhibition of this process is described in the present paper. Sodium fluoride, iodoacetic acid, norvaline, phenylserine, 5-bromuracil and 2-thiouracil did not inhibit the root formation completely. Complete inhibition, however, was observed after treatment of pea stem sections by kinetin, ethionine and chloramphenicol (5 X 10^-5 M, 1 x 10^-2 M, and 1 x 10^-2 16 hours after sectioning). The concentration of kinetin which produced complete inhibition of root formation simultaneously stimulated the growth of the lateral buds.
Root formation under the conditions described below can be divided into two stages. The first stage 64 hours from the beginning of the experiment, the second stage 64 hours later. Further, the first stage includes the formation of the meristematic cells in the pericycle areas. In the second stage are included the growth of roots and differentiation of root-tissues. Roots were formed, first of all, in the short vertical region of the sections near to the basal buds. Secondary xylem formation was also observed during the cultivation of the sections. This process was stimulated by kinetin.

Immediate response of water uptake by intact plants ofPisum sativum L. to the introduction of high concentrations of α-naphtaleneacetic acid (NAA), β-indoleacetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid (MCPA), coumarin was determined by a series of potometric measurements. Growth substances were present in the root medium in two concentrations: 10^-3 m and 10^-2 m; the concentration of coumarin was 5. 10^-4 m and that of EDTA was 10^-3 m.
The response of water uptake to the application of the growth substances and coumarin was always negative. EDTA did not affect immediately the intensity of water uptake. The inhibition of water uptake brought about by the growth substances takes place immediately. Coumarin causes slow, progressively increasing inhibition of water uptake. A coincidence was found as to the time course of the changes in the water uptake intensity in the presence of high concentrations of growth substances and coumarin in the root medium with the time course of changes of transpiration intensity, found under analogous conditions by Allerup (1964). This may be considered as another justification for the hypothesis, according to which the rapid changes of transpiration intensity in the presence of high concentrations of growth substances in the root medium are caused by rapid changes of the intensity of water uptake.

The differentiation of tissues is closely connected with the proteosynthesis. One can therfore assume that tissues with different types of cell growth (meristematic or elongation growth) and with different degrees of differentiation are different in their protein composition. In order to compare the protein composition of different plant organs, the method of disc electrophoresis on a polyacrylamide gel has been used by some authors. As compared with other methods used up to now, e. g. isolating proteins on DEAE cellulose or in Sephadex, this method does not need so much material and its resolution ability seems to be higher. It is also quicker and enables the study of several samples simultaneously. Its disadvantage is that proteins can be identified mainly by means of Rf and their quantity, measured from the intensity of staining of individual fractions in the gel, which may be misleading due to different sorption capacity of different proteins (FričFričová 1967). None the less, it is good for comparison of protein composition of individual parts of the plant body.
Different methods have been used to compare protein composition of individual growth zones in roots.Barsky,Ivanov andPushakova (1965) used luminiscence microscopy and found that in maize roots it is not possible to find substantial differences by this method.Morgan andReith (1954) arrived at similar conclusions. On the other hand,Steward et al. (1965) andMorris (1966) found qualitative differences in protein composition of different parts of pea roots using acrylamide electrophoresis. The results of the last named authors show considerable discrepancies in details, due perhaps to a different method of extraction (buffer, pH, purifying method).
We have used acrylamide gel electrophoresis for investigating proteins in precisely defined growth zones of theVicia faba root.

1. Protein synthesis in pollen tubes ofNicotiana alata Link etOtto estimated by the incorporation of leucine-¹⁴C is linear over six hours of artificial cultivation after a short lag phase. 2-Thiouracil and other growth-stimulating antimetabolites of natural pyrimidines and purines, such as 6-azauracil, 5-nitrouracil, 8-azaguanine and 8-azaadenine, stimulate the incorporation of leucine-¹⁴C into protein. The intensity of stimulation of protein synthesis is associated with the intensity of growth stimulation by antimetabolite.
2. Synthesis of RNA is inhibited by 2-thiouracil (according to the incorporation of uracil-¹⁴C, orotic acid-¹⁴C and³²PO₄ ^3- ).
3. Chloramphenicol (25 and 250 ppm) decreases during a one-hour treatment of pollen tubes the incorporation of leucine-¹⁴C by 12 and 24%, respectively. The same inhibition is found in pollen tubes stimulated with 2-thiouracil.
4. Pollen tubes incorporated 2-thiouracil into RNA. Stimulation of growth by 2-thiouracil can be reversed with uracil or uridylic acid.
These findings are related to the present views on protein synthesis and the mechanism of the chloramphenicol effect especially with respect to the possible explanation of the stimulation of protein synthesis during a simultaneous inhibition of RNA formation.
Physiological resistance of pollen tubes toward RNA antimetabolites, the relatively low sensitivity toward chloramphenicol, the contradictory change in RNA and protein synthesis due to 2-thiouracil and, further, resistance toward actinomycin D (Tupý, Süss 1965) point to the stability of the complex of messenger RNA with ribosomes in pollen tubes.