1. The complete life history of C. flexuosa has been investigated by the author for the first time on the basis of cytological observations and on the formation of reproductive swarmers. 2. Stages of meiosis are found occurring preceding the formation of quadriflagellate zoospores. Biflagellate gametes are formed as a result of mitotic divisions. This leads to the conclusion that C. flexousa possesses a life history of isomorphic alternation of generations, similar to C. pellucida as reported by Foÿn (1929). 3. The process of nuclear division during mitosis follows a normal course and the number of chromosomes has been estimated 24 from the mitotic metaphase which is the diploid number of this sp. Number of 12 bivalents has been estimated during meiosis. 4. The morphology of the chromosomes in regard to the position of centromeres has been studied. The chromosomes show median and submedian centromeres. In the meiotic bivalents, the numbers of chiasmata have been traced out. Out of 12 bivalents, 7 bivalents show one chiasma each and the rest 5 bivalents show two chiasmata each. 5. The detailed morphological characters of the present marine sp. have been studied. The width of the main filaments of C. flexuosa (Griff.) Harv. seem to vary from 80μ to 185μ. 6. Besides morphological characters i.e. the dimension of the filaments and the type of branching, shape and size of the reproductive swarmers appear to be specific for definite spp. and can also be helpful in distinguishing species of Cladophora. 7. The sp. of Cladophora can also be distinguishable in the dimensions of the resting nuclei and in the sizes of the chromosomes. 8. The method of staining by acetocarmine has been used throughout the investigation for cytological study.
1. In the electron micrographs of root hair cells of Azolla imbricata, the following intracellular organellae were observed. 2. In the vacuoles, a number of heavily electron-dense bodies are seen. They appear to be aggregates of particles of ca. 30mμ in diameter and probably of lipid nature. 3. The mitochondria show features of the typical structure of those described in plant cells. 4. The plastids in cells treated with osmium fixatives appear to be composed of lamellae and grana-like structures. The plastids in cells fixed with permanganate show the piles of several short lamellar structures, i.e., grana-like structures, but show no so-called lamellar structures. 5. The endoplasmic reticulum is seen irregularly winding in a shape of discrete layers or in stacks of lamellar layers. Palade granule-like bodies are seen in osmium-fixed cells, but not demonstrated in permanganate-fixed cells. 6. The Golgi-like structures are composed of cisternae, and small discrete vesicles are often found at the edges of the cisternae, which appear more clearly in permanganate-fixed cells than in osmium-fixed ones.
Pteris vittata sporelings were centrifuged at 2- and 3-cell stages of the protonema at 500 to 50, 000 times gravity. When a centrifugal force was exerted towards the basal direction of the protonema tip cell, the chloroplasts and nucleus were stratified in its basal end. In further culture of these basally centrifuged materials, an outgrowth occurred at the basal portion of the tip cells almost at 100 per cent, when the centrifugal force was stronger than 5, 000 times gravity and the length of tip cells was more than 300μ. Such an outgrown cell continued to develop as a branching, finally giving rise to a mature gametophyte. Thus the original developmental axis was altered, and the original tip was basalized, sometimes forming a rhizoid at its apical portion. A discussion was given of aspect that the developmental polarity of this fern protonema is controlled by the localization of endoplasmic components rather than by the cortical cytoplasm which is hardly movable by centrifugation.
Incorporation of tritiated thymidine, tritiated cytidine, tritiated DL leucine and the autoradiograph technique were used to determine the patterns of synthesis of DNA, RNA, and protein throughout the complete mitotic cycle of pea root meristem cells. Pulse experiments with tritiated thymidine were used to determine the duration of the G1, S and G2 period. The incorporation of tritiated cytidine into highly polymerized RNA required from 3 to 4 hours. No RNA was synthesized during metaphase and anaphase. A possible relationship between the nucleolus, nuclear membrane and RNA synthesis was discussed. Protein synthesis was at a high level throughout the entire cycle with the G2 period being most active.
The karyotypes of three forms of Oryza perennis i.e. barthii, balunga and a collection from Assam were investigated by pachytene analysis. The three karyotypes are comparable in the relative lengths of the chromosomes but differ in the arm ratios. This species exhibits the most symmetric karyotypes in the genus, balunga being included in the group 2b and other two varieties in the group 1b of Stebbins' (1958) classification.
The spherical cytoplasmic granules of Hydrodictyon reticulatum of 0.5-1.0μ in diameter were stained by Nile blue and showed an intense fluorescence when excited by long wave length ultraviolet light. When these granules were stained with berberine sulfate and excited, they did not show any fluorescence. Therefore, these granules are different from the so-called spherosomes of Perrier since they showed no fluorescence after staining with berberine sulfate. The ground substance of the cytoplasm showed an intense yellow fluorescence after staining with berberine sulfate. Differential centrifugation showed that this fluorescence of the cytoplasm is emitted from the microsomes. In this study, spherical cytoplasmic granules as well as microsomes were distinguished from other cell inclusions by fluorescence analysis with these two dyes.
Chromosome numbers and meiotic behavior of species and hybrids in the Nigrohirsutae section Dendrobium were investigated. The chromosome number of the Philippine species, D. schuetzei and D. sanderae was 2n=40, while that of the extra-Philippine species, D. formosum and D. draconis, was 2n=38. The chromosomes of D. formosum were about twice as large as those of D. sanderae, and those of D. draconis were intermediate in size. Meiosis in D. schuetzei and its hybrids with D. sanderae and D. dearei was regular with the formation of 20 bivalent chromosome at metaphase I. The triploid hybrid, D. sanderae×D. dearei, formed 19-13 trivalents and 7-1 bivalents and univalents. D. dearei×D. formosum, having 39 chromosomes, exhibited 19-11 bivalents with a mean of 15.9, most of which were heteromorphic. It can be concluded that the Philippine species are very closely related to each other while D. formosum is more distantly related.
Presence of polyphosphates in the cells of several blue-green algae was established by staining with toluidine-blue and lead nitrate-sulphide techniques. It was shown that during the development of spores the metachromacity of the granules was lost. It was suggested that depolymerization of the long chained polyphosphates could be the reason.
Mice explsed to 12, 24, 43 and 74 r gamma radiation per day were observed with reference to the following features and compared with comtrols: testis weights, testis areas in section, tubular areas in section, Chalkley counts on cell types and on empty space within and surrounding the tubules, and special counts of type A and intermediate spermatogonia, type B spermatogonia and leptotene spermatocytes. The results show that under prolonged gamma irradiation testis weights decrease concomitantly with the loss of spermatogenic cells from the tubules. Measurements of cross sectional areas of testes and tubules were found to decrease along with testis weight. There is an increase in the relative area occupied by Sertoli cells surviving the gamma doses, because of decreasing tubular dimensions. Spermatogonia under 12 and 24 r/day survive with low levels of mitotic activity. At higher intensities they do not survive beyond 2000 r cumulated dose. Spermatocytes vanish due to lack of recruitment as well as through irradiation death. Their disappearance time is intensitydependent. The same is true of spermatids and spermatozoa.
Chromosomes were counted at meiosis and mitosis in 4 sapogenin-bearing species of Dioscorea and 9 other species. Chromosome numbers of 7 New-World species are reported herein for the first time. In these, 2n numbers were 36 except in two lines of D. floribunda which contained 54-chromosomes and showed irregular meiosis. All New-World species counted had chromosome numbers which are multiples of 9, whereas all Old-World species had numbers which are multiples of 10. The significance of the findings is discussed with reference to origin and distribution of the genus, processes of speciation, and possible barriers to breeding.
Failure of association of homologous chromosomes at diakinesis and metaphase I was observed in two sterile plants of pepper in the first generation following X-irradiation of the pollen. The degree of asynapsis differed in the two plants. Univalents were more frequent in the X1 plant from the 2000 r treatment than in the plant isolated from the X1 following exposure of the pollen to 500 r. Irregular distribution of chromosomes was observed at anaphase I, telophase I and during the second division. The spores derived from a single microsporocyte were often atypical in size and number; micronuclei were evident in many of the spores.
Chromosomes of fhe Northeastern American Woodchuk, Marmota monax were studied. Two animals had consistently a 2n value of 38 with 12 metacentric pairs. The Y-chromosome is the smallest element and it is submetacentric. Sex chromatin could not be identified with certainty in the histologic sections of all major organs.