Changes in the nuclear structure of bacteria, particularly during spore formation

Changes of nuclear structure in bacteria have been studied by means of the hydrochloric acid-Giemsa method which produces brilliantly stained specimens and can be carried out with almost the same ease as some of the ordinary routine staining techniques.The nuclear changes in the four spore-bearing organisms studied are outlined in Text-fig. III, to which the following numbers refer. The dumbbell bodies which are dispersed in the cells of the young growth (1) become alined in the long axis of the cell (2) where they eventually fuse into an axial nuclear cylinder (3, 4). These cells divide up into fusion cells of approximately the same length (5). The development of the ‘chromosome’ stage (1) into the fusion cell (5) is the first step in the process of sporulation. During its further development the fusion cell or spore mother cell divides twice (6, 7), with the result that it is segregated into four structures which often assume dumbbell shape. Therefore the chromatin cylinder of the individual spore mother cell seems to be equivalent to four nuclear elements one of which functions as the spore ‘chromosome’ (‘nucleus’?), whereas the remaining three disintegrate (8, 9). The ripe spore (9) representing, as it does, the smallest cell unit contains one nuclear structure only.Therefore the two main features in spore formation of bacteria appear to be (1) a fusion of the dumbbell bodies into an axial chromatin rod (‘autogamy’?), (2) a reduction partition which is reminiscent of, though not corresponding to, the more complicated phenomenon of meiosis in the higher organisms. The sporulation, as outlined in this paper, gives new proof of the important part played by the chromatinic dumbbell bodies (‘chromosomes’) in the developmental cycle of spore-bearing organisms. The fusion cell with its axial chromatin cylinder has for the first time been proved to have a progressive functional significance as a stage in a nuclear cycle. The particular mode of fusion followed by reduction partition suggests that the chromatinic dumbbell bodies may be concerned with the transmission of the hereditary characters in bacteria.

Evidence on spiral structure and chromosome pairing in osmunda regalis L

The present work is in the nature of an essay on certain aspects of chromosome structure which have been impressed upon me by prolonged study, with a variety of technical methods, of chromosome behaviour in one plant, Osmunda regalis . The tissue to be examined has been principally that of the developing sporangium, supplemented by observations on roots and prothalli, which, however, will not be referred to on this occasion. The sporangium itself offers ample material for the study of both mitosis and meiosis since the development from the young archesporium to the ripe spore is a rapid and continuous one. The technical methods employed are principally three, that of sections, that of the aceto-carmine squash (Manton 1937), and Sax and Humphrey’s modification of the ammonia method for spiral structure. Each of these methods if used by itself has limitations which necessarily result in an incomplete picture; each, however, has certain powers peculiar to it, and, as will be shown, the dovetailing together of information from all three provides a body of evidence which to me personally has been most illuminating. I am, however, fully conscious of the innumerable pitfalls with which the subject abounds and am prepared to find that some of my observations and deductions may need modification. Nevertheless, since a comparable body of evidence does not appear to exist for any other cytologically worked organism the risk of error is perhaps worth taking.

Memoirs: Gonospora minchinii, n. sp., a Gregarine inhabiting the egg of Arenicola

The new species of gregarine described above, and to which we have given the name Gonospora minchinii, occurs in the coelomic fluid of the female Arenicolaecaudata. The adult trophozoite is pear-shaped, and the ripe spore has a thin cyst without distinct funnel. The young trophozoite lives in the egg floating in the coelomic fluid of the Arenicola, where it grows at the expense of the food-material stored in the ovum. To reach the ovum it pierces the vitelline membrane and perivitelline layer. The growing trophozoite occupies a deep depression it causes in the egg, to which it adheres by its epimerite. The margin of this depression becomes drawn out into delicate protoplasmic processes. The cytoplasm and nucleus of the host-cell, and also the development of the perivitelline layer, are affected by the presence of the parasite. When full-grown the trophozoite escapes from the egg by a hole pierced in its envelopes, and leucocytes then enter the space so left to complete the destruction of the ovum.