Fine structure of the integument in the silkworm larvae was studied in thin sections with electron microscope, using ‘S mottled’ strain. In the outer endocuticle dense bands of laminae having average thickness of 0.3μ ranging from 0.2 to 0.4μ were observed, and the dense bands are made up of double layers. From the light and electron microscopical studies on the cuticle of the silkworm, it has been postulated that Ito's ‘wedge-shaped structure’ should be called pore canal. The pore canals in the silkworm are arborescent near their outer ends, and the shape is similar to that of Ephestia and Diataraxia. They are 2-6μ in diameter and 10-20μ in length, and filled up with filamentous substance. In some parts of the endocuticle, thread like substance which has the appearance of micro protrusion from epidermal cell was observed in the electron micrograph. Dense bodies supposing to be composed of melanin pigments or osmophillic substances such as lipoprotein, were observed only in the outer endocuticle of the melanin pigmented part. In the epidermal cell, mitochondria showing similar structure to that of other insects or mammals were observed. Besides, unidentified bodies, which may be called ‘granulated bodies’ are observed in the cell.
1. The investigation was made to study the differential nature of the chromosomes and other cell components on the basis of their phosphatase activity. 2. To test alkaline phosphatase activity, Gomori's revised method and for acid phosphatase activity, Glick and Fisher's adaptation of Gomori's method were applied. 3. Differential precipitation has been very high in all the cellular components in case of alkaline phosphatase, while with acid phosphatase the activity has been very low and uniform. 4. In polyploid cells the nucleoli are practically indistinguishable, other cellular components giving the same reaction at a much reduced rate. 5. The high alkaline phosphatase activity is due to the presence of this enzyme in both nucleic acid and protein components of the chromosomes. 6. End portions of chromosomes contain a higher dosage of the enzyme. In the constriction regions it is insignificant, but the satellite thread is positive in some of the plates. This implies that satellite stalks and secondary constriction segments which are functionally similar, may differ in the quantity of phosphatase positive substances or nucleic acid. 7. Decreased phosphatase activity in polyploid cells is due to the greater dispersion of the enzyme as a result of increase in cell surface. 8. Loss of distinction of nucleoli in polyploid cells is the result of diminution of viscosity difference between the nucleoli and nucleoplasm caused by chemical treatment.
The chromosome conditions were investigated in four cases of acute and subacute myelogenous leukemias and one case of chronic myelogenous leukemia of man based on the bone-marrow technique, and they were compared with normal somatic chromosomes. The results have indicated that in each leukemia under study there occur stem-cells which contribute to the growth of the leukemia. Those stem-cells show a rather small variability of chromosome number and morphology from normal somatic cells. The chromosome number mode was found to be 44 to 46 for case A, 44 to 45 for case B, 44 for case C, 46 for case D and 44, 45 to 46 for case E. Detailed observations have revealed that there occur morphological changes of chromosomes due probably to structural changes in leukemic cells. Generally the sexelement, particularly X-element, is entirely undetectable in leukemic cells. Virus-like particles, 118mμ in average size, were detected by electron microscopy in leukemic cells infiltrated in liver tissue of a patient having chronic myelogenous leukemia. The occurrence of virus in relation to the development of leukemia was considered.
Vegetative nuclear division in Ophiostoma fimbriata is not morphologically similar to ordinary mitosis. Nuclear division in this fungus is also different to that described in the vegetative mycelium of the related ascomycetes Neurospora crassa and Gelasinospora tetrasperma. In O. fimbriata the nucleolus is left out in the cytoplasm and does not divide together with the chromatin. Chromosomal complexes have been observed during the second vegetative division. These configurations do not appear to be aligned on a metaphase plate nor is there any visible evidence for the presence of a spindle. Added Note: Since the submission of this report further studies on the vegetative nuclei in O. fimbriata have revealed that towards the end of division the chromatin appears as an irregularly-shaped, double bar or strandlike configuration. Examples of such configurations are shown in Figs. 12 and 13, though in Fig. 12 they appear too densely stained to be properly resolved. At the end of division these strands, which lie almost parallel to each other, do not slide apart in opposite directions nor do they separate to “opposite poles”. They divide transversely at their midregions, usually one before the other, and then their extremities move apart in a manner comparable to that shown in Figs. 9, 15, and 30. A more detailed report describing the morphology and suggesting the significance of these configurations in a number of fungi is being prepared for publication at a later date.
The materials of P. secans that have been studied represent several different pseudogamous, obligately apomictic clones of the species. The microspore meioses are characterized by a uniformly high degree of asyndesis and the usual occurrence of restitution nuclei. An upset in timing relations of the processes involved in division is suggested by wide variation in the time of initiation of meiosis among the microsporocytes in an anther, complex chromosome movements in many cells, and irregular cleavage of some cells at various stages of chromosome behavior. Restitution nuclei may be formed at any stage after diakinesis, with the stage at which they occur apparently having a general relationship to the time at which division was initiated in that cell relative to other microsporocytes in the anther. The initial movement of the univalents is toward the poles of the spindle, and is sometimes completed with the formation of telophase nuclei that remain distinct. In most microsporocytes, however, the movement toward the poles is followed by a movement of the chromosomes toward the equator. At a later stage which is found in some cells the univalents at the equator can be seen in process of division. This division may result in the splitting of many univalents, but soon afterward breaks down with the formation of a restitution nucleus. Although some irregularities were observed, the post-restitution division is usually regular and results in the formation of dyads of unreduced microspores.
The elongation of protonema cells and rhizoids of bracken was studied by the direct measurement of shift of marks which were made on wall surface with the micromanipulator. Those cells showed a typical tip growth. The apical cell of protonema elongates chiefly in its apical dome, very slightly in the region more than 10 microns from the apical end, and not at all in the region over 30 microns from the apical end. Some of the subapical cells elongate and make the tip growth, but their elongation is less than that of the apical cell. The third cell, less often than the subapical cell, grows slightly at its apical end. The fourth cell does not elongate. There exists the polarity, from apex to base, of the possibility and ability of elongation not only in each protonema cell but also in a protonema as a whole. The nearer to the apex the given part is, the larger the possibility and ability of elongation are, and vice versa. Rhizoids elongate at the part within 1 micron or less of their tip.
Two heterozygotes were found in A. fistulosum (2n=16), one for a deficient satellite and one for a reciprocal translocation. 1. In the unequal arm of the deficiency heterozygote a single chiasma but not more than one was formed at MI in 80.4 percent of the cases; the frequency of equational AI separation attained to 79.5 percent. 2. In the translocation heterozygote, two pairs of chromosomes were distinguished, each being heteromorphic as to the lengths of the long arms. Frequencies of a single chiasma, but not more than one, formed in the long arms of the two pairs were 77.9 and 48.3 percent of the cases, respectively. In good conformity with these values, the frequencies of equational AI separation of the two pairs were 74.6 and 46.3 percent respectively. 3. These two findings are in very good agreement with the chiasmatype hypothesis accounting for the cytological configuration of the chiasmata.
Chromosome behavior in 2n=20 species of Dichanthium Willemet indicates that they are functional diploids. Tetraploids (2n=40) appear to be segmental allopolyploids. Hybrids between two tetraploid races of the same species or between different species are characterized by 2n=40 or 2n=60 chromosomes. Morphological data indicate that the cytologically reduced as well as unreduced female gamete may be fertilized by a normal male gamete. Both the cytologically reduced as well as the unreduced embryosac in the hybrids may develop parthenogenetically to form viable offspring. From a cytological study of these “polyhaploid” plants and their hybrid parents it becomes clear that autosyndesis is the common mode of pairing in Dichanthium Willemet. It was also established that chromosome pairing may take place within the basic genome (n=10), indicating that the original basic number for the genus could have been n=5.
A case of translocation induced by the effect of Bassia oil in maize seed has been studied. Examination of the pachytene figures has shown that an interchange involving two short unequal segments has occurred between the 4th and 7th chromosomes. The cytology of this plant including the various chromosome associations, chiasma distribution and segregation has been studied. In about 18.8 percent of the diakinesis figures rings or chains were found, the rest showing 10 separate pairs. Counts of pollen grains showed very little sterility. This is due to the higher frequency of figure of 8 configuration of the ring and consequent segregation of alternate chromosomes to the same pole.
The behaviors of chromonemata, nucleoli and endosome during the division of the macronucleus in the living Chiamydodon peclarius have been observed by the phase contrast microscopy. 1. The chromonemata have appeared at prophase with the extrusion of the nucleolar materials, which have been masking the chromonemata. 2. The chromonemata of the organism do not develop into usual chromosomes at metaphase, and their characters resemble the endornitotic chromosomes of Heteroptera and Drosophila. 3. The division apparatus including the polar caps and central substance, which are responsible for the chromonemata movement, is produced with the transition of the endosomal substance during metaphase to early anaphase. 4. The extrusion of the nucleolar materials takes place at prophase, late anaphase and telophase, and the diffusion of the peripheral substance of the metaphase macronucleus has observed. 5. The mechanism of the protrusion of the nucleolar materials has been discussed with emphasis upon the increasing of the nuclear materials at prophase and the change consequent upon it of the structure of the macronuclear membrane.
1. Development of Avena chloroplasts in normal, etiolated and chlorophyll-deficient mutant plants, are observed with an electron microscope. 2. Normal proplastids in green plants have one or two plastid centers, from which fine double lamellae of about 80Å in thickness protrude radially, fused each other at the end and formed a sack-like structure. Then the lamellae arrange parallel through the plastid and form ordered layers composed of the fine lamellae. As the number of lamellae in one layer increases, grana are differentiated within certain areas of these layers. Grana are composed of staks of discs of double membranes (grana-lamellae, each of which is about a 80Å in thickness). Each disc is connected with one stroma-lamella of about 300Å in thickness which is often resolvable as doublet. 3. In etiolated and albino leaves, plastid developments are stopped at certain stages of differentiation, and grana can not be formed. This suggests that these structural blockings may be associated with the failure of chlorophyll synthesis. 4. In both pale green mutants, mutant 602-15 which is a hybrid between A. strigosa and A. barbata and mutant 3250 caused by X-ray irradiation, plastids develop and grana differentiate, but plastid development is somewhat different between them. While in the mutant 602-15, the completion of lamellar system is followed by destruction caused by vacuolization, in mutant 3250 arrangement of lamellae is abnormal from the early stages and grana arrange irregularly in direction and in localization in mature chloroplasts.