Comparative cryoscopic determinations of osmotic pressure and the refractive index of cell sap were analyzed with the aid of correlation coefficients and characteristics of the trend of their course (by means of the slope of the regression lines and probability field). It was confirmed that an indirect estimation of the osmotic pressure of the cell sap is readily feasible refractometrically and that it is sufficiently reliable if a relationship between the two values is determined experimentally in advance. The biological homogeneity of the material tested influences this relationship, both genetic and ontogenetic. This conclusion followed from the evaluation of the correlation between osmotic pressure of cell sap and its refractive index in leaves ofHordeum sativum Jessen. The significance of biological homogeneity was brought out by the classification of all measured pairs of values into groups according to varieties and according to leaf insertion.

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.

1. Suppressors were found in reciprocal crosses of some varieties of barley for the manifestation of recessive and dominant alternatives of the following characters: number of rows of the spike, presence or absence of glumes, character of awns and formation of the spike basis.
2. A proof of the existence of suppressors is presented merely statistically on the basis of segregation ratios in the F₂ generation, in the total F₃ generation and in the individual segregating progenies of plants from the F₂ generation and in the back crosses.
3. It was confirmed that the inheritance of the characters investigated is independent in spite of the fact that the segregation ratios are complicated by the participation of suppressors.
4. Separated cultivation of individual progenies from hybrid seeds formed on the mother plant was shown to be very suitable and efficient in hybridization experiments of this type.
5. The significance of the participation of the suppressors in the inheritance of the characters studied is pointed out with respect to the practical breeding of barley.

1. A comparison of the immunochemical similarities in the proteins legumin and vicilin and the albumin fraction of pea seeds (Pisum sativum Poir), was carried out.
Legumin and vicilin are globulins with different physical properties, but probably with a certain degree of immunochemical similarity as shown by serological cross reactions.
Albumins from the pea seeds, on the contrary, have not only different physical properties but they also do not even show any immunochemical similarity to globulins.
2. Immunochemical specificity of legumin and vicilin in the globulin fractions of the seeds of further species of the familyViciaceae was sought: in representatives of the genusLens, Vicia, lathyrus, Pisum, Cicer, Medicago, Trifolium, Lupinus, Phaseolus andGlycine.
Legumin and vicilin more or less similar to that of peas are present in all the observed representatives of the tribeVicieae (that is in some species of the genusPisum, Lens, Vicia, Lathyrus, Cicer); in observed representatives of the tribeTrifolieae (i.e. in species of the genusMedicago andTrifolium) the only protein is similar to vicilin; in investigated species of the tribeGenisteae andPhaseoleae, proteins similar to legumin and vicilin are missing.
In all observed representatives of the tribeVicieae (Pisum sativum Poir,Lens culinaris Med.,Lathyrus clymenum L.,Lathyrus sativus L.,Lathyrus silvester L.,Lathyrus odoratus L.,Vicia faba L.,Vicia sativa L.,Cicer arietinum L.), indications of leguminoid and vicilinoid protein characters are present in varying degrees and thus even here no cases resembling loss mutation of protein characters were discovered. The following generalisations may thus be made: the tribeVicieae is characterised by the presence of leguminoid and vicilinoid proteins (or proteins rather like them): the tribeTrifolieae is characterised by the presence of proteins similar to vicilin: in the tribeGenisteae andPhaseoleae, leguminoid and vicilinoid characters are missing. Because of the similarity of proteins in the tribesVicieae andTrifolieae, closer phylogenetic relations can be assumed to exist between the tribesVicieae andTrifolieae than between the tribesVicieae andPhaseoleae orGenisteae.
3. Legumin and vicilin are at the same time examples of protein characters with a relatively wide occurrence (these protein characters rather resembling each other are present in all the representatives of the related genera and tribes studied).
4. Further it can be assumed on the basis of unequal distribution of the proteins legumin and vicilin in the related tribes investigated (vicilin has a wider occurrence), that both proteins have not developed in parallel, but that they apparently are of unequal phylogenetic age. And it may be concluded either that vicilin is relatively a more primitive protein character than legumin or that phylogenetic differentiation of legumin was relatively more rapid than such differentiation of vicilin.

Die Entwicklung der Samenanlage des Weizens (Triticum aestivum L. var.erythrospermum cv. Niva, Früjahrssorte) von der Befruchtung der Eizelle bis zur völligen Reife des Getreidekornes haben wir beobachtet. Auf Dauerpräparaten beobachteten wir die Bildung der Fruchthülle und der Samenschale. Wir konnten feststellen dass sich die Fruchthülle im erwachsenen Getreidekorn eng an die Samenschale anlegt, von der nur eine einschlägig, mit einer Kutikula bedeckte Schicht erhalten bleibt. Epidermis und Hypodermis wachsen nicht it den Querzellen zusammen, sondern trocknen nur an; man kann schwer von einem Verwachsen sprechen, wenn der Teilungsprozess sein Ende gefunden hat und dort, wo die Gewebeschichten durch eine Kutikula getrennt sind..

In the course of six years, pollination interrelations and self-pollination ability were investigated in seven more important Sour Cherry (Cerasus vulgaris Mill.) cultivars grown in Czechoslovakia. The success of pollination was evaluated according to the percentage of fully ripened fruits. A survey of results obtained is given in Table 1.
Reciprocal incompatibility was found between two cultivars (De Olivet, Brune de Bruxelles). Thus, the first incompatibility group in Sour Cherries has been established. The other varieties form combinations with different degrees of compatibility. The varieties studied are listed in Table 2 according to their general fertility and pollinating ability.
Complete autosterility was found in two cultivars (Körösi, Brune de Bruxelles), two others, on the other hand, showed a very high degree of self-fertility (Morello, Griotte de Vít). These two varieties also render the best results when intercrossed. The remaining cultivars (De Olivet, Griotte de Vacek and Ostheimer) are only very little self-fertile and need the presence of good pollinators to ensure a satisfactory crop.

1. Die Antherenlänge ist beiLilium henryi kein Massstab für das im Innern der Antheren ablaufende Stadium der Pollenmeiose und Pollenentwicklung. Es bestehen signifikante Unterschiede zwischen den Antheren-Längen gleicher cytologischer Stadien zu verschiedenen Zeitpunkten der Vegetationsperiode.
2. Durch amperometrische Titration bei 0° C in Stickstoffatmosphäre konnte in Extrakten des Tapetums und des Archespors eine zyklische Änderung im Gehalt an Thiol-Gruppen während zweier Vegetationsperioden gefunden werden. Der Sulfhydrylgehalt zeigte, bezogen auf den Stickstoffgehalt, synchrone Maxima im Pachytän und nach der Tetradenbildung.
3. Bezieht man die mg Äquivalente SH auf mm der Antherenlänge, so ergeben sich für das Archespor Maxima in der Diakinese und in der Metaphase 2, während im Tapetum Maxima des SH-Gehaltes während der Diakinese, kurz vor dem Tetradenzerfall und während der Einlagerung des Pollenfarbstoffes defunden werden. Daraus wird auf einen Transfer von SH-Gruppen aus dem Tapetum zu den Mikrosporen während der Metaphase 2 geschlossen.
4. Eine Änderung des Gehaltes an SS-Gruppen konnte während der Pollenmeiose und Pollenentwicklung nicht beobachtet werden.
5. Der grösste Teil der ermittelten Thiol-Gruppen liegt als Glutathion vor, während eine weitere SH-Verbindung, die nicht mit Cystein identisch ist, wahrscheinlich als Peptid vorliegt.
6. Auf einen meiose-induzierenden Effekt der SH-Verbindungen konnte aus vorliegenden Messungen nicht geschlossen werden.

Transpiration rates of leaf blades of irrigated and not irrigated spring wheat plants were studied in relation to the water content and growth changes in the test plants during their development. The applied irrigation stimulated the growth and slightly delayed the development of the test plants. It increased chiefly the water content and to a lesser degree the dry solid weight in the plant body. The quantitative and qualitative properties of the water content in the plant affected not only transpiration rates, but also the development of new and the dying off of old organs and tissues, especially of leaf blades. Transpiration rates in irrigated plants were markedly higher than in not irrigated plants. Mean transpiration rates of different leaf blades varied and were typical for each leaf blade. From the static aspect it was possible to express and even to explain some of the relationships and the heterogenity of the leaf blades on the same stem by the "Law of Zalensky". This involved mainly the mean values of growth characteristics and the investigated features of the water regime. On the other hand, from the dynamic viewpoint it was possible to divide the different leaf blades according to their transpiration changes into two groups. The first group includes the blades of the first to third leaf, the second group the blades of the fourth to sixth leaf and the ear. The capacity to control the water regime in the different blades is greatest at the stage of tillering, shooting and milk ripeness. During these developmental stages the marked decrease in transpiration, caused in the first place by a number of internal and not only external factors, was explained.

A method suitable for serial determinations in genetic experiments is described. Colorimetric determination of HCN (by 1-phenyl-3-methyl-5-pyra-zolone and pyridine, phenolphthalin or sodium picrate) facilitates processing of samples releasing 0.2 μg to 20 μg of HCN. Before hydrolysis of the glycoside the oil content in the seeds can be determined. Variance analysis of the cyanogenic properties of the particular seeds of two sorts of flax with an average HCN content of 0.4 and 0.9 μg shows that the differences between plants and between capsulae of the same plant can be determined.

The intensity of photosynthesis and the content of chlorophyll were estimated in disks cut out from different areas of fodder cabbage leaves (var. Coulet de Flandre). The content of chlorophyll per unit area was higher in the apical than in the basal part and in the central than in the peripheral part of the leaf. No significant differences were observed in the intensity of photosynthesis in samples removed from different parts of the leaf. The intensity of photosynthesis is not directly proportional to the dry weight of the sample although the dry weight per unit area is considerably higher in the apical than in the basal part of the leaf area.

The cytological effects of the insecticide Systox on the primary roots of Vicia faba and possible mutagenic effects on Arabidopsis thaliana have been studied. It was found that a 0.02% watery solution of Systox after a testing period of 3,6 and 9 hours under partially anaerobic conditions gives the following results:
a) no inhibition of mitosis was produced;
b) inhibition of the spindle was produced independently of the duration of action of Systox;
c) the occurrence of chromosomal aberrations increased significantly after 3 and 6 hours without restitution and after 3 hours with restitution for 24 hours. The frequency of these aberrations may depend on the isomeration of Systox in water since in older Systox solutions-where, according to data in the literature the concentration of isomer II increases-the frequency of chromosomal aberration increases significantly after 24 hours restitution. This influence of isomeration, was not found to affect the inhibition of the spindle, mentioned above.
Partial anaerobiosis itself produces a significant increase in inhibition of mitosis after 6 and 9 hours, an inhibition of spindle formation and an increased occurrence of chromosomal aberrations as against 3 hours testing.
After the action of a 0.2% and 1% concentration of Systox for 6,48 and 72 hours on seeds of Arabidopsis thaliana no chlorophyll or other mutations in the M₁ and M₂ generation were found.

Für die Versuche haben wir Rhizone der Ackerquecke (Agropyrum repens L.) und die Frühjahrsweizensorte Niva verwendet. Die Versuchskulturen haben wir in Sand in Mitscherlichgefässen und in Komposterde im Garten durchgeführt. Die gemeinsame Wachstumdauer von Quecke und Weizen erstreckte sich im ganzen auf rund 30 Tage. Es wurde das Wachstum von Quecke, sowie Wachstumsintensität und Zuckergehalt der oberirdischen Teile der Weizenpflanzen festgestellt.
Die Versuchsergebnise zeigten, dass das Wachstum der Weizenpflanzen umso tiefer absank, je intensiver die Quecke in den Kulturgefässen anwuchs und ebenso sank der Wassergehalt der oberirdischen Weizenteile; auch der Glyzidegehalt erlitt kenntliche Veränderungen. Die Atmungsintensität stieg bei Anwesenheit kleiner Queckenmengen in den Gefässen grösstenteils etwas, während sie in Gegenwart grösserer Queckenmengen ein wenig absank. Im Vergleich zum Wachstum erschien sie aber sehr wenig beeinflusst. Hieraus geht hervor, dass die Produktivität der Atmungsprozesse unter dem Einfluss von Quecke stark herabgesetzt erscheint. Um diese Veränderungen gründlicher zu klären, ist ihr weiteres Studium von nöten.

When small branches of different plants were dipped after cutting into a solution of humic acid, a brown substance penetrated into vessels and coagulated there. The vascular bundles were stained to the height of 1-6 cm after a week. The presence of the humic acid in the parenchymal cells could not be demonstrated directly, but cells with a yellow or brown cell wall remained alive (they could be plasmolysed).
Humic acid, labelled with C¹⁴ was distributed in the same way in sterile and in non-sterile plant cultures, mainly through vascular bundles.

Seeds of apple and pear trees were found to contain 0-5-0-7% tryptophane expressed per dry weight. The hydrolyzate of the seeds contained tryptophane demonstrable microbiologically. Exogenous tryptophane applied to apple-tree shoots toward the end of the vegetation season gives rise to a new compound. Its R_F in isopropanol : ammonia : water (10 : 1 : 1) was found to be 0.08, in butanol : acetic acid : water (4:1:5) 0.25.

In dieser Arbeit wurde die Wachstumswirksamkeit von zwanzig, meist neu synthetisierten und an Pflanzen bis jetzt noch nicht geprüften Derivaten VII bis XXVI der Phenoxyessigsäure verfolgt. Es handelte sich um Substitutionsderivate und auch um Derivate, die durch Umwandlung der Karboxylgruppe hergestellt wurden. Die Struktur und die Wirkung der 2,4-Dichlorphenoxyessigsäure (I) Wurde bei diesen Versuchen als Standard verwendet. Die Wirkungslosigkeit der geprüften Substanzen in der Koncentration 10^-6 (1 mg pro Liter) auf keimende Senfpflanzen(Sinapis alba L.) wird infolge Strukturänderungen, auf die Struktur von 2,4-D (I) bezogen, besonders was die Art und Zahl der Substituenten am Phenylrest betrifft, erklärt.

The authors have studied the anatomy of the apical meristem in axils of the highest pair of leaves in chickweed [Stellaria media (L.) Vill.]. The shoot apices in the axils of highest leaves start to grow at different times; this is one of the causes of the unequal development (different length and thickness) of the branches. This unequal development is repeated also in branches of the second, third orders etc.

The present paper is concerned with inheritance of the development of lateral florets in crosses of two-rowed forms of barley of the distichon type with the six-rowed forms of types vulgare and brachyurum.
The character can be employed for identification of true hybrids as early as in the F₁ generation in crosses of two and six-rowed forms when the two-rowed character is dominant. Unsuccessful crosses can thus be eliminated in time. The character can also be useful for the determination of linkage ratios in higher hybrid generations.
1. Heredity of the development of lateral florets in spikelets of barley spike was investigated during hybridization of two-rowed and six-rowed forms by means of the method for continually variable characters.
2. The results obtained indicate that in the manifestation of the character, nuclear factors of two types take part, i. e. the more numerous factors of lesser effect, (here apparently also belong the pleiotropic effects of factors for other characters), and the less numerous factors of greater effect which appear to be fairly independent of the alleles for the number of rows in the spike.
3. It seems that extranuclear factors participate in addition to the nuclear as suggested by the inequality of reciprocal crosses in the same combination.
4. The modifiability of the degree of character manifestation due to external factors is great in hybrid plants.

The test for cold survival in two lines of maize on alternately changing the sterility of grains and soil revealed that for the given type of seeds the death in cold soil is mostly due to epiphytic pathogenic microflora, followed in importance by soil pathogenic microflora and finally by the direct influence of cold.

Experimental investigations on the course of yellows-type virus infections in plantsTrifolium repens L. gave the following results:
During 24 and 48 hours after the completion of the test feeding period the clover phyllody and clover dwarf viruses spread in the plant maximally up to 5 cm. from the point of inoculation.
In the infected plants, the reproduced clover phyllody and clover dwarf viruses appeared on the average 5-6 days earlier than disease symptoms.
Acquisition feeding of leafhoppers onT. repens plants infected with the clover dwarf virus for different periods of time, revealed a decline in the virus concentration in the plants after 45 days from the appearance of disease symptoms. In plants infected with the parastolbur virus, this decline was not found.

One of the criteria employed for evaluating the resistance of plants to drought is their ability to endure the effects of water deficit with no irreversible changes in their tissues. This ability was investigated by means of a method described in this paper. The leaves of some xerophilous grasses (species of the genusStipa, Melica, etc.) were left to dry up under precisely defined experimental conditions so that they reached various degrees of water saturation deficit. Then they were cut up into segments and-mounted in a special frame-were saturated with water. The initial deficit and its compensation were investigated gravimetrically. The resultant values were plotted on a graph. Whereas in some instances the water loss from the leaves during desiccation was linear, the compensation curve exhibited a characteristic breaking point which indicated the degree to which the water loss could be compensated, and when the changes became irreversible. It was found that the studied series of plants of typical continental species have the capacity to supplement their water content ad integrum even in the case of considerable water deficit. Plants living in regions of a more oceanic type do not exhibit this property. It is probable that this property will also be of much value in the explanation of causal phytogeography.

Some constructional adjustments of leaf chambers for photosynthetic rate measurements of leaves and spikes of cereals are described.

In jarowisierten und nicht jarowisierten Karyopsen einer Winter- und einer Sommerweizensorte wurden die auxin- und gibberellinähnlichen Stoffe chromatographisch bestimmt. Die Chromatogramme wurden biologisch ausgewertet. Bei der Wintersorte wurden in Bezug auf die Verteilung der Wuchsstoffe keine Unterschiede zwischen der jarowisierten und nicht jarowisierten Variante festgestellt. Bei der Sommersorte bestanden solche Unterschiede. Auf Grund der Versuchsergebnisse wird angenommen, dass die Unterschiede zwischen beiden Varianten der Sommersorte auf eine unspezifische Wirkung der niedrigen Temperatur zurückzuführen sind und dass der Jarowisationsprozess in keinem kausalen Zusammenhang mit einer Veränderung des Wuchsstoffgehaltes steht.

StrainsAspergillus amstelodami No. 5,A. chevalieri A 24 andA. ruber No. 71 were maintained for 21 generations on wort and on Czapek's medium with 20% sucrose by means of monoconidial isolation. A gradual increase in conidium formation was observed which was different on the two media. No decrease in the formation of perithecia or their disappearance could be observed. In strainsA. amstelodami No. 5 on wort andA. ruber No. 71 on Czapek's medium with sucrose, three morphological changes could be detected, characterized first of all by retarded growth and delayed differentiation during the first days of incubation and by reversibility to the original phenotype in some colonies during subsequent generations.A. chevalieri A 21 displayed two different phenotypic changes on wort medium, the changes appearing to be characteristic and permanent. They are accompanied, in addition to other morphological features, by retarded growth and delayed differentiation during the first days of incubation.
The present results are compared with those ofJinks (1954, 1956) and the origin of the changes observed and the effect of media is discussed. As concerns the reversible changes it can be assumed that they are of extranuclear origin since it appears to be justified to rule out changes caused by the mutation of the genome and by segregation of nuclei due to heterokaryosis. With changes where no reversion can be observed the origin is not clear. Increased sporulation is ascribed to changes in the cytoplasm.

Of twenty common oligosaccharides, monosaccharides and sugar alcohols tested, raffinose was found to be the best substrate for growth and respiration of apple pollen tubes. While in a solution of sucrose growth is retarded after about six hours, accompanied by a decrease in respiration intensity, no such decrease was observed in pollen tubes cultivated in a solution of raffinose even after 10 to 20 hrs. of growth. Raffinose is inverted by pollen tubes much more slowly than sucrose which is taken as the cause of the long-term effect of raffinose. Pollen did not germinate at all in a solution of turanose.
It thus appears to be probable that the primary factor in the specific effect of sucrose and raffinose on the growth of apple-tree pollen tubes is the presence of β-D-fructofuranose in the sugar molecule.

Chromatographic analysis of wheat leaves grown for 4 to 10 days in a solution of gibberellic acid (10-20 p.p.m.) revealed a higher level of fructose-1,6-diphosphate as compared with that of 3-phosphoglyceric acid and phosphoenolpyruvic acid, and of 3-phosphoglyceric acid as compared with that of a hitherto unidentified phosphate. These changes were found under different light regimes which preceded extraction of phosphates from leaves. On the basis of these data and in view of earlier results (Luštinec, Pokorná, Růžička 1962) it is assumed that glycolysis interacts with reactions utilizing its intermediate products for the synthesis of lipids, this representing a possibility of bringing about changes in leaf phosphate levels due to gibberellic acid. In order to verify the postulate the incorporation of 1-¹⁴C- and 6-¹⁴C-glucose into lipids, phospholipids (the magnesium salts of which are insoluble in acetone), carbon dioxide and the non-lipid fraction of leaves was investigated. It appeared that the incorporation of 1-¹⁴C into the lipid fractions of plants grown for 3-7 days in a gibberellic acid solution is markedly lower than that of 6-¹⁴C. The ratio of radioactivities C₆∶C₁ was increased in the lipids by the three-hour treatment of leaves with gibberellic acid (10 and 50 p.p.m.) during their incubation with glucose-¹⁴C. In view of the fact that the amount of substances extractable with ether is the same in the experimental and in the control leaves and that the incorporation of 1-C into lipids is frequently considerably higher in the controls than the incorporation of 6-C the effect of gibberellic acid on the rate of exchange of carbon atoms between the lipids and the products of glucose catabolism should be borne in mind.

Ascorbate oxidase was studied as one of the terminal oxidases in the roots of seven-day old squash cultures (Cucurbita pepo L.) in relation to calcium nutrition and the influence of calcium deficiency on the quantity and quality. The work led to the following conclusions:
1) Ascorbate oxidase was identified inCucurbita pepo L. roots, sort "Kabačky". Identification was carried out according to substrate oxidation, and the sensitivity of enzymes to 10^-4 M DIECA; the possibility of interference by other oxidase systems was eliminated during the study of the oxidation reaction by the use of acetone preparations.
2) Dependence of the activity of enzyme on pH, temperature and concentration of the substrate was determined and the stoichiometry of the reaction (1/2 mol. O₂ per 1 mol. ascorbic acid) was verified.
3) Activity of enzymes of cultures, cultivated in a complete nutritive solution ("NS") and calcium deficient ("-Ca") solution, and changes in activity during the development of cultures, were compared. Converted into fresh weight, the activity of the "-Ca" variant is significantly higher (about twice) than that of the "NS" variant. In both cases, however, it was sufficient to cover the O₂ consuption of intact roots. Qualitative differences in enzymes of the two variants were not determined.
4) Cytochromoxidase may participate in the oxidation of ascorbic acid in the roots. Participation of polyphenoloxidase was not proved. With the intermediation of ascorbic acid, ascorbinoxidase can oxidize hydrogen-SH-groups of cysteine.
5) Addition of ascorbic acid to root tips causes a considerable rise in QO₂ (by to 90%), therefore activity of oxidation systems of ascorbic acid is not fully used in intact cells during endogenous respiration.

Bei der Sichtung meines reichen Materials von mixoploiden Wurzelspitzen habe ich Wurzeln gefunden, welche sich des polyploiden Sektors dadurch zu entledigen schienen, dass sie sich in einen diploiden und einen polyploiden Teil spalteten. Die Abspaltung von polyploiden Zellsträngen kommt zwar häufig vor, in den hier beschriebenen Fällen bildet jedoch der diploide Sektor eine neue Wurzelspitze, der polyploide Teil stellt allmählich sein Wachstum ein, während die neu differenzierte Wurzelspitze weiter wächst. Auch das ist eine Art von Bereinigung und Diploidisierung der mixoploiden Wurzelspitze. Sie setzt allerdings voraus, dass die Wurzelspitze etwa zu einer Hälfte meist aus diploiden, zur anderen meist aus polyploiden Zellen besteht. Es findet dann im Urmeristem der diploiden Hälfte eine Umdifferenzierung zur selbständigen Spitze statt, wogegen der polyploide Spitzenteil allmählich oder plötzlich die Teilung seiner Zellen einstellt, sodann sich eine Zeitlang streckt, dann aber zerrissen wird und abstirbt. Ich konnte einige solche Fälle schon in ihren anfänglichen Stadien beobachten. Der Vorgang ist nicht auf den eutelischen Typus beschränkt.

The previously found (Slavík, 1959) distribution pattern of osmotic pressure of cell sap in the area of the leaf blade of dicotyledonous type which is independent of the water balance and unchanged even with zero diffusion pressure deficit, was complemented by further data concerning the physiological heterogeneity of the adult leaf blade ofNicotiana sanderae hort. in relation to water relations and CO₂ exchange.
The transpiration rate from the intact leaf surface was found to be about 50 to 70 per cent lower in the apical part of the blade than in the basal part. The natural permanent water saturation deficit was found to be about 10 per cent lower in the apical part. The stomata density in tobacco as well as in sugar beet leaves were on an average 40 per cent lower in the apical part, their size being here 30 per cent higher. The relative index of the area of the stomata pores (density × square of the pore length) did not differ significantly in the two places. The photosynthetic rate (per area) in fully water saturated leaves was found to be 17 per cent lower in the apical part of the blade, the chlorophyll content (per unit area) being greater in the thicker apical part. Respiration rate measured manometrically as Q_O2 was significantly lower in the apical part, both when calculated according to area and to dry weight (12 per cent). Similar but much lower differences were found between the edge and the central part of the leaf blade.
This physiological heterogeneity and polarity of the leaf blade originating in the ontogenesis of its extension growth is causally based on the different relative hydration levels. Thus the study of various physiological processes in different parts of the leaf blade is suitable for the investigation of their relationship to different hydration levels.