An intensive cytological study was made of chromosome behavior at anaphase I in 12 intervarietal hybrids of cultivated rice. Two types of unusual behavior were found, bridges without fragments and bridges accompanied by acentric fragments. Since bridges without fragments were also found in each of 3 homozygous varieties in approximately the same frequency as in the hybrids, it was concluded that this behavior was not abnormal and did not indicate the presence of structural differences in chromosomes. Bridges accompanied by fragments were found at very low frequencies in 9 of the 12 hybrids, indicating the presence of paracentric inversions. These results provide proof of widespread structural differentiation in the chromosomes of cultivated rice varieties and suggest strongly that the partial sterility which occurs commonly in intervarietal hybrids is caused by complex inversions of the included type.
1. The spermatogenesis of the Indian apple-snail, Pila globosa Swainson has been described in this paper. 2. The spermatozoa are of two types, viz., the uniflagellate eupyrene and the multiflagellate oligopyrene. Only the eupyrene sperm has been described in detail. 3. Late spermatogonia and the spermatocytes reveal filamentous and granular mitochondria and a single duplex sphere. 4. The single duplex sphere divides into two by binary fission both during mitosis and meiosis. 5. In the spermatid the single duplex sphere secretes a small granular acrosome which later becomes conical. The duplex sphere is sloughed off. 6. The mitochondria of the spermatid fuse to form 6 to 8 balls. These later on elongate and form ribbon-like structures which give rise ultimately to the mitochondrial sheath of the middle-piece. 7. The head of the eupyrene sperm is also spirally twisted. 8. The oligopyrene sperm in this prosobranch is stumpy and short bearing 4 to 8 flagella. The cylindrical nucleus bears a small cap-like acrosome. The small middle-piece seems to be devoid of the mitochondria.
Chromosome aberrations at meiosis and the microspore division were studied for 24 species and varieties and ten interspecific hybrids of Gasteria. All were diploids with 14 somatic chromosomes. Meiotic abnormalities at first metaphase were significantly more numerous in two of the hybrids and one of the species than they were in the other hybrids and species. Inversion bridges at first anaphase showed no significant difference. Microspore aberrations were fairly numerous in only one plant, a hybrid, and the difference between the species and hybrids was not significant. Pollen fertility was high in most of the species but significantly lower as a whole, in the hybrids. The species hybridize readily and the comparatively low frequency of aberrations coupled with the higher sterility of the hybrids indicates that differences exist largely at the genic rather than at the chromosomal level.
1. The testes of Anopheles stephensi sensu stricto are two pale yellowish, ellipsoidal bodies. Their wall consists of an outer, tough, pigmented envelope, and an inner squamous epithelial layer. The nuclei of various types of resting cells within the testes are characterized by a peripheral, basophilic crescent. The anterior part of the testicular cavity is divided into cysts which hold spermatogonia and primary spermatocytes. Germ cells at later stages of differentiation are held free within the posterior part of the testicular cavity. 2. The spermatogonial metaphase configuration consists of two pairs of V-shaped autosomes and a pair of unequal, subtelocentric sex chromosomes. The homologous chromosomes exhibit somatic pairing. The centromeres appear as distinct, non-staining gaps. The centromere is slightly off-median in one of the autosomal pairs. 3. The nuclei of early primary spermatocytes show long, slender, chromomeric threads and a peripheral basophilic crescent. The latter subsequently resolves into deeply staining thread-like structures representing the heterochromatic regions of the sex chromosomes and a lightly staining nucleolar body. The chromosomal threads undergo a process of uniform condensation to produce thick pachytene bivalents. The nucleolus disappears by diplotene. The sex chromosomes associate together only along short lengths of their long limbs proximal to their centromeres. Terminalization of chiasmata takes place during diakinetic condensation of the chromosomes. The sex bivalent is symmetrical. The metaphase spindle is formed within a welldefined nuclear space surrounded by a thin limiting membrane. Tiny dotlike centrioles are present. At first anaphase the autosomal univalents disjoin normally. The sex chromosomes, on the otherhand, show obligatory postreduction. The sex chromosomes lag during the first anaphase separation. In the dyads the chromatids are widely divergent except near the centromere. The telophase nuclei are oval in shape and show a peripheral concentration of chromatin. 4. A short interkinesis stage is present. At the second prophase the dyads appear as typical X or cross-shaped figures. Subsequently they constitute a tangled group at the centre of nucleus representing a prometaphase stage. A second metaphase plate is produced although the stage is of short duration only. The sex chromosomes show precession during the second anaphase. The spermatid nuclei fall into two classes on the basis of the relative dimensions of their heteropycnotic dots.
1. The diploid chromosome number in the males of this species is 46. The fundamental chromosome number is also the same. 2. No metacentrics have been observed in the karyotypes of this species. It is being reported for the first time for ophidian karyotypes. 3. Meiosis is normal. First and second metaphases show 23 bivalent and univalent chromosomes, respectively. Males are homogametic. 4. Possibility of the occurrence of M-A+A type of process is discussed.
1) The suitability of the chromosomes of the Bluebell, has made it possible to study the composition of the individual chromosome-number classes at pollen-mitosis in the triploid of Endymion hispanicus (Mill) Chouard. 2) Present studies show that the Anaphase chromosome classes and the Pollen-grain groups may not be ‘pure’, but may contain all 3 of one chromosome or lack all 3 of a particular chromosome. 3) In the triploid Bluebells the Pollen-mitosis showed an apparent increase in groups with more than 1.5n chromosomes, and it has been shown that a number of this is caused by the ‘impure grains’. The presence of these grains is due to delay in disjunction at Anaphase I. 4) The individual chromosomes in a triploid occur with different frequencies in the population, the highest being the smallest Chromosome H followed by one of the long but satellitic Chromosome D. The lowest is Chromosome B. 5) A number of the above features of chromosome behaviour in the triploid is shown to play some part in the sterility of this type of polyploid.
In vertebrate oocytes the presence of a nuclear membrane can be established in fresh as well as in fixed materials studied by light and electron microscopy. Using various techniques the membrane can be demonstrated in three dimensions as an in vivo entity of such cells. The evidence presented supports the conclusion that a morphological nuclear membrane is present in all cells but can be demonstrated only by using specific techniques suitable to the specific cell. The author wishes to thank Drs. S. T. Piliero and Dr. E. L. House of New York Medical College for there critical reading of this paper and Mrs. House for technical assistance rendered as well as Mr. E. Harbilas for executing the drawing of Fig. 10.
1. The chromosomes of six Melaniid snails have been studied. The chromosome numbers of the various forms are as follows. Melania crenulata _??_ 2n=34+X=35 Paludomus tanschaurica _??_ 2n=36+XY=38 Melanoides tuberculatus (diploid race) _??_ 2n=32 Melanoides tuberculatus (polyploid race) _??_ and_??_ 90-94 Melanoides lineatus _??_ and _??_ .............71-73 Melanoides scabra _??_ ..................76-78 2. The chromosomes of all the Melaniids studied are metacentric and in this respect their chromosome complements are similar. 3. All the Melanoides except the diploid race of M. tuberculatus are high polyploids and these add to the only one instance of polyploidy so far known in Molluscs. 4. The co-existence of parthenogenesis and polyploidy may account for the numerous forms of Melanoides, their variability, wide distribution and consequent taxonomic difficulty. In view of the prevailing confusion in identification and nomenclature of the Melaniids in general, a cytotaxonomical approach seems imperative. An indication of this is provided by the two races of M. tuberculatus. 5. The two cytologically distinct races of M. tuberculatus though not markedly different with respect to size and external morphology do show ecological physiological and biochemical differences. Polyploidy seems to confer hardiness and selective advantage.
1. The present investigation was carried out with a view to observe the effects of certain chemicals on endosperm nuclei of Cestrum diurnum Linn. 2. Saturated, half saturated and quarter saturated solutions of Resorcinol, Pyrogallol, Phloroglucinol and 8-Hydroxyquinoline in distilled water were injected below the main stalk of the flower clusters and period of treatment was varied with varying concentrations. The period of treatment varied from one hour to twenty-four hours. 3. The general effect was the production of stickiness, fragmentation of chromosomes, resulting in the lethality of the twig. 4. Of all the chemicals tested, 8-Hydroxyquinoline had less toxic effect, while Pyrogallol and Resorcinol had high toxic value. 5. Polyploidy noted in certain cases after Pyrogallol treatment showed the presence of narcotic effect. Subnarcotic and lethal effect too in endosperm nuclei were recorded. 6. With Phloroglucinol, lethality was the final result of treatment though death of the twig did not result instantaneously. It was brought about gradually after prolonged period. With low concentration and short period of treatment, more time was taken by the twig to reach lethality and with the prolonged treatment, the toxicity caused was comparatively rapid. 7. In general, fragmentation of the chromosomes was not observed in any concentration following one hour treatment, while with prolonged period of treatment of three hours, five hours and twenty-four hours, increasing amount of fragments was observed. This may indicate that a definite amount of fluid level within the cell is required to cause fragmentation of chromosomes. 8. The effect of chemicals tested here on endosperm nuclei differed from effects of these chemicals tested on roots by other workers, indicating thereby that differential cytoplasmic constitution of the different organs may account for their behaviour.
The kinetics of the induction by ultraviolet radiation of extrachromosomally inherited respiratory deficiency in Saccharomyces is determined by the ploidy level of the cells. The fraction of the inducing radiation damage which is photoreactivatable is similarly ploidy dependent. These findings are taken to indicate that the primary radiation events which result in inactivation or loss of the extrachromosomal genetic determinants of cellular respiration are nuclear in nature.
The nuclei in the germ tubes and mycelium of the imperfect fungus Phyllosticta sp. do not divide in a manner directly comparable to ordinary mitosis. A mitotic apparatus such as a spindle or metaphase plate was not observed. At the beginning of division the granular chromatin contracts usually forming a tightly packed complex of filaments. Counts of these filaments could not be made. As division proceeds this complex elongates, constricts at the midregion and at the end of division the extremities pull apart forming the chromatin portions of the sister nuclei. During division the original central body becomes separated from the dividing chromatin and progressively smaller. At the end of division the central body is either a tiny remnant of its former self or has completely disappeared. New central bodies are formed in the maturing sister nuclei.
The evolution of diverse morphological forms in Convolvulus pluricaulis Chois. was found to be mainly due to intraspecific polyploidy. The tetraploid showed thick and large leaves with a higher leaf index. An increase in the size of stomata, epidermal and palisade cells was associated with tetraploidy. The number of stomata and epidermal cells per unit area was inversely proportional to the euploid increase in chromosome number. The tetraploid which was late in flowering further characterised itself by an enlargement in flower, pollen and seed size. The pollen fertility in diploid as well as tetraploid was above 95 per cent. The chromosome numbers of diploid and tetraploid were determined as n=9 and n=18, respectively. The details of meiotic division in the two have been described. The cytological data in conjunction with morphological studies suggest that the tetraploid in all probability arose as a result of autopolyploidy or segmental polyploidy.