The exodermis of ash roots is initiated early in the apical meristem. When fully differentiated, it is composed of alternating "long" and "short" cells measuring approx. 70×25×25 μm and 25×28×25 μm respectively. At a short distance from the apex, the long cells undergo structural and histochemical changes from a "primary" towards a "secondary" stage: an impermeable suberized lamella is formed, cellulose lamellae become impregnated by lignin, and the protoplast dies off. The short cells show a distinctly thickened outer wall ("cap") which is composed exclusively of cellulose, and possess abundant cytoplasm with a large nucleus. In the process of ageing the structure of short cells is not markedly affected. Following the early disintegration of rhizodermis, the exodermis works as the external protective layer of tho fragile end-root. Its long cells fulfil the mechanical protection, the short cells serve as passage cells for solutions and gases, during the whole life-span of the rootlet.

The water loss of leaves of the same level of insertion but of various ages was examined. The results show that the transpiration of youngest leaves is higher than that of the older ones. The oldest leaves which have started yellowing show an increase of transpiration. This is probably related to the premortal changes of the leaf. The differences are probably caused by various physiological states of leaf because the leaf area was not different.

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.

Several methods of NA isolation and estimation were examined in order to determine RNA in the whole root systems of young wheat plants. It was found out that during the hydrolysis of roots with perchloric acid according toOgur andRosen (1950),Spirin (1958) andHeitefuss (1965) a considerable amount of orcine-positive compounds is released which cannot be adequate to the RNA content. Therefore the separate RNA determination in the presence of DNA was excluded even after the NA fractionation by hydrolysis at various temperature and perchloric acid concentration. Besides NA hydrolysates contained a high amount of other compounds absorbing in the UV-region. Compounds interfering with both these methods were present especially in the basal parts of roots.
Using the method ofKern (1960) a nucleoprotein fraction was isolated containing about 75 per cent of the total NA content in the tissue. This fraction consisted of more than 90 per cent RNA combined with proteins, namely the ribosomal RNA. After the hydrolysis it could be estimated spectrophotometrically for the hydrolysate did not contain other compounds absorbing in the UV-region. In the root tips the content of this fraction was high in comparison with the basal parts of roots and it changed with the kind of nutrition.

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 site of anaerobic respiration in the latex is the serum. The main respiratory substrate is fructose. The CO₂ formation in serum is increased by additional fructose on the average about 2.5-3 times. Glucose does not influence CO₂ evolution by serum but slightly increases O₂ consumption.
With respect to sugars, latex serum contains essentially only sucrose and a low amount of raffinose. During the incubation of serum sucrose is hydrolysed, the fructose component is immediately utilized in respiration and glucose accumulates.
The rate of CO₂ formation in latex as influenced by fructose is negatively related to the rubber content of the latex. Latex with a high rubber content reacts only slightly or not at all on additional fructose.
The main limiting factors of latex respiration and sugar utilization are the following:
1. The deficiency of substrate, due to low activity of β-fructofuranosidase.
2. The rate of glucose phosphorylation (D'Auzac, Jacob 1967).
3. Presumably the low activity of phosphoglucoisomerase.
4. The rubber content of the latex.
5. The concentration of CO₂ in latex; this factor may be important in vivo, in the laticiferous system.

In this paper we compare the influence of heterologous and isologous DNA on the radiation damage repair of primary root meristematic cells ofVicia faba. Roots, irradiated by exposure of 150 r were cultivated at different time intervals either in tap water, or in a solution of heterologous or isologous DNA. In comparing mitotic activity of meristematic cells it was found that both types of DNA studied enhance the recovery of irradiated cells. The frequency of postmetaphase chromosomal aberrations of irradiated cells was influenced also by post-irradiation action of exogenous DNA. While heterologous DNA exhibited synergical effect with radiation in the sense that it increased the post-irradiation incidence of aberrations in all time intervals studied, isologous DNA had a strong repair effect-the application caused a significant decrease of the percentage of post-metaphase aberrations. Both kinds of DNA caused changes in the relation of chromosome to chromatid aberrations; a higher percentage of chromatid aberrations was registered. The study of the distribution of aberrations between large and small chromosomes ofVicia faba showed that the post-irradiation application of heterologous DNA increases damage of small chromosomes while isologous DNA caused an increased repair ability in this chromosomal group.

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.

An investigation was conducted to study the interrelation of free amino acid metabolism and root formation in etiolated pea stem sections as dependent on time and on inhibition of root formation by kinetin and ethionine.
The rise in the level of aspartic acid and increase in the rate of conversion of¹⁴C-labeled glucose to free amino acids were found to be characteristic features of the formation of foci of meristematic cells in pericyclo region. The formation of roots was reflected, in general, much more in the rate of conversion of labeled glucose to free amino acids than in the levels of corresponding amino acids.
The total amount of free amino acids was not significantly changed during incubation of stem sections in a solution of kinetin (5×10^-5 m). A rapid fall in their level was recorded in the next 24 hours. The incorporation of¹⁴C from glucose into a precursor of lignin, phenylalanine, was completely inhibited by kinetin which stimulated simultanously the growth of adjacent buds. Stimulation of secondary xylem formation, which appeared later, was accompanied by the resumption of¹⁴C-incorporation into phenylalanine.
Inhibition of root formation by ethionine resulted in the rapid fall of the level of most amino acids and in a significant decrease in the rate of incorporation of¹⁴C from glucose into amino acids. A decreasing level of ethionine in tissues during cultivation of ethionine-treated stem sections was accompanied by a gradual rise in the individual amino acids and in the rate of conversion of glucose into free amino acids.

The Czechoslovak isolate produced symptoms characteristic for viruses belonging to the rattle group. A virus variant comparable to Köhler's "Wintertyp" appeared to be present. Two predominant particle lengths of 90 and 191 nm were found in purified preparations. The virus reacted with Dutch TRV antiserum.

In the experiment with 18 winter varieties the genotypic, phenotypic and environmental correlations were estimated in all combinations between the pairs of 11 quantitative characters.
Both yield of grain with its components and further characters were evaluated, of which flag leaf size and leaf angle of the last but one leaf are of importance for the utilization of light energy and consequently for receiving maximum rates of photosynthesis.
In simple genotypic and phenotypic correlations their different stability with regard to mineral nutrition, eventually to the date of sowing was proved.
In the discussion the limited signification of simple correlation for the statement of complicated processes in plants caused by multiplied associations of characters was pointed out. In the example of yield components of the plant at the application of 60 kg N per hectare it was shown that also further unknown variable factors might participate in the genotypic correlation. It may be concluded that the inclusion of them when constructing the selection indexes will give further foundations for handling yield as a breeding or genetic character, and for the causal analysis of yield formation in wheat.

A gasometric method was developed for measuring water deficit in leaves. For a leaf at full turgor the amount of water penetrating into the tissue after removing the air from intercellular spaces by means of a vacuum pump, is equal in volume to the gas removed from the intercellular spaces. In a leaf with a water deficit the amount of the infiltrating water is greater than the removed gas volume by the amount egual to the water deficit. Determination of the volumes of the gas removed and penetrating water enables water deficit, if any, to be calculated. Comparative measurements carried out on five plant species confirmed the correctness of the method suggested. Reduction of the measuring time allowed to eliminate completely the sources of errors associated with the growth of tissue and loss of dry weight during respiration.

Identification trials were carried out to determine what virus causes a mosaic disease of sweet peas in Czechoslovakia. The found properties of the identified sweet pea mosaic virus, the character of its transmission and its host range prove that sweet peas in Czechoslovakia are attacked by common pea mosaic virus (CPMV). Some insignificant differences in properties between our virus isolate and CPMV were observed in the course of the determination of properties of our virus isolate on various host plants. The possible existence of more strains of CPMV is discussed. The transmission of sweet pea mosaic to the plants ofPhaseolus vulgaris L. was negative. For this reason bean yellow mosaic virus (BYMV) was eliminated as a possible pathogen of our virus isolate. At the same time the indicator plantsChenopodium giganteum Don. andChenopodium guinoa Willd. with eight developed leaves were established to be most suitable for the determination of the properties of the isolate by the half-leaf test. The transmission of the virus isolate by seeds was not proved.

Im Wasserextrakt der zerriebenen BlattläuseBrachycaudus napelli Schrk. befinden sich phytotoxische Stoffe, die durch einen biologischen Tomatensprosstest untersucht werden können.
Bei Erwärmung der Aphidenextrakte von 125°C sowie bei zweistündiger Erwärmung der getrockneten Rückstände bei 105°C blieb die Phytotoxizität von denselben unverändert erhalten.
Die phytotoxischen Stoffe sind aus dem Aphidenhomogenat sehr gut mit Wasser, gut mit Äthanol und Azeton, dagegen gar nicht mit Diäthyläther, Benzol und Chloroform bei Zimmer-temperatur extrahierbar.
Durch Dialyse wurde aus dem Blattlausextrakt eine kleinmolekulare Fraktion abgetrennt, welche an Testtomaten Blattnekrosen hervorrief. Die andere, im Dialysierschlauch zurückgehaltene höhermolekulare Fraktion, rief bei den Testpflanzen Welkeerscheinungen hervor, die mehr auf eine mechanische Verstopfung der Leitgefässe der behandelten Pflanzen hindeuteten.
Entwickeltes Extraktionsverfahren: thermolabile Stoffe wurden durch Erhitzen, lipoide Stoffe durch Ätherextraktion und höhermolekulare Stoffe durch eine Dialysemembran von den Aphidenhomogenaten entfernt und phytotoxische Stoffe in grob gereinigter Form mittels Wasser- und Azetonextraktion gewonnen.

The content of the carbohydrates glucose, fructose and sucrose was determined in spring barley anthers at different stages of maturity. During maturation the sucrose content of the anthers increased markedly. The following 17 free amino acids were detected in anthers of different stages of maturity: aspartic acid, glutamic acid, serine, alanine, arginine, leucine, isoleucine, lysine, α-aminobutyric acid, glutamine, proline, tyrosine, phenylalanine, valine, threonine, cystine and glycine. Quantitative analysis was only carried out in amino acids present in higher concentrations in the analysed samples. These were: aspartic acid, glutamic acid, α-aminobutyric acid, proline, serine, valine and glutamine, and a mixture of amino acids (leucine, isoleucine, valine and phenylalanine). The total content of free amino acids increased with increasing maturity of the anthers. However, not all amino acids followed contributed to this increase, but only proline, glutamic acid, aspartic acid and glutamine. A small difference was found in the variety Gopal in which the aspartic acid content did not increase significantly, but the content of the mixture of amino acids and serine did. With the exception of green anthers of the variety Firlbecks Union, proline was present in the highest concentration in all samples analysed.

The effect of temperature on the number of lesions and the time of their appearance was studied by inoculating French bean leaves (Phaseolus vulgaris L. cv. Perlička) with lucerne mosaic virus either 24 or 48 h before or, 24 or 48 h after they were exposed to various temperatures. The temperatures tested were 23, 25, 27, 30, 33 and 36° C.
Before and after such exposures the plants were kept in a constant temperature of 25° C. By increasing the temperature before inoculation the number of lesions increased in comparison with the control. The optimal temperature for the maximum number of lesions is between 27° and 30° C. There is no significant difference between those experiments when the exposure time was 24 h or 48 h before inoculation. The same temperatures applied for 24 or 48 h after inoculation have a decreasing effect upon the number of lesions formed by LMV on French bean leaves. The decrease is 30 to 75%. In this case the first necrotic local lesions appeared 42 h after inoculation when exposed to higher temperatures above 27° C for 24 h, and 60 h after inoculation when exposed to these temperatures for 48 h. The shape of lesions varied a little in both cases as the pictures show.

In Wurzelhomogenaten aus Keimlingen der Modellpflanze Sinapis alba L., die durch Pyridinderivate in der Konzentration 5×10^-4 M beeinflusst worden waren, wurden Aktivitätsänderungen der Glucose-6-phosphat-Dehydrogenase gefunden: Phenäthylpyridine (IA, B, C) und trans-Styrylpyridine (IIA, B, C) steigern die Enzymaktivitätin vivo, in vitro führen sie jedoch zu einer deutlichen Hemmung. Der dritte Strukturtyp, Pyridylphenazetylene (IIIA, B, C), istin vivo zwar unwirksam, doch in denin vitro Versuchen war er noch wirksamer als die beiden vorher genannten Typen. Es ist wahrscheinlich, dass die Ursache der Enzymaktivitätssteigerung in der Steigerung der NADP-Biosynthese liegt. Die Erhöhung dieses Koenzyms kann den Kohlenhydrateabbau zu Gunsten des oxydativen Mechanismus, des Pentosecyclus, zur Folge haben.

Labelled carbon dioxide was supplied for 22 hrs to a leaf of the leader or to the lateral shoot in two-year-old apple seedlings. The distribution of radioactive assimilates within the plant following this treatment was investigated by using radioautography.
The transport of labelled assimilates from the young leaf of the leader was very meagre and affected only parts of the stem and the leaves situated in the close vicinity of the treated leaf.
The¹⁴C-labelled assimilates from the mature leaf of the leader were transported in a considerable amount to the apex and to the other leaves of the leader. They were also found in an appreciable amount in the stem and the roots, as well as in some lateral shoots.
After supplying¹⁴CO₂ to the lateral shoot remarkable transport of labelled assimilates was observed. Radioactivity was detected in the tip and in the youngest leaves of the leader, as well as in the roots. Their path in the stem was studied by dissecting the plant and examining the cross section from each internode. This method revealed that the assimilates from the treated leaf or shoot were transported downward only on one side of the stem in a helical pattern. The lateral shoots situated on the radioactive side of the stem were also labelled, whereas those situated on the opposite (non-radioactive) side were not labelled.

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 Euonymus Mosaic Virus was isolated fromEuonymus europaea. The virus was transmitted by sap to cucumber and other test plants, by seeds orAphis euonymi F., and it was soilborne, too. The sap from cucumbers lost its infectivity after 10 minutes at 80°C and after 35 days at 20-22°C. It is probably a new virus so far not described. The investigations of this problem are not finished, yet.

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.