Div ision of protoplast 



9 



authors as occurring in the ' central body ' are probably due to pathological 

 conditions and occur in cells which are undergoing degeneration. 



Division of the protoplast. On the division of the cell there is much 

 evidence to prove that the incipient nucleus divides without any mitosis 

 such as is understood in fully differentiated nuclei. There is a constriction 

 of the incipient nucleus, but the only suggestion of mitosis, even in the 

 most highly developed species, is a slight tendency of the net- work to become 

 drawn out in parallel lines, though the meshes are not broken except by the 

 advancing constriction (fig. 6). The pre- 

 sumed chromatin granules do not divide 

 during this amitotic division, but an ap- 

 proximately equal number is found in the 

 two parts after division. There are in the 

 numerous members of the Myxophyceae 

 various degrees of differentiation of the 

 nuclear structure, which may account for the 

 fact that the division has been interpreted 

 in so many diverse ways. In some cases 

 the constriction of the incipient nucleus 

 takes place before the appearance of any 

 division of the protoplast as a whole, and 

 the view held by Macallum that the 'central 

 body ' initiates division is in these cases 

 probably correct. In Chroococcus macro- 

 coccus there may be a twice-repeated division 

 of the primitive nucleus before there is any 

 sign of the division of the cell itself. In 

 the Chroococcaceoe division of the cell occurs 

 by a gradual constriction, either at the time 

 of division of the primitive nucleus or subsequent to it. There is no septum 

 laid down. On the other hand, in many of the Myxophycese with cylindrical 

 filaments a transverse septum is formed on division, and the inward growth 

 of this septum gradually divides both cytoplasm and primitive nucleus into 

 two more or less equal parts. 



The nuclear mitosis described by Kohl (consult fig. 7), Olive, and Phillips is probably 

 of the nature of an illusion since it is quite easy to imagine the presence of mitotic figures 

 in stained preparations of the dividing cells of many of the Blue-green Algee. There is, 

 however, such a mass of evidence to the contrary that the mitotic figures of supposed 

 dividing nuclei published by these authors must be considered as the result of uncon- 

 scious self-deception. 



That the central differentiation of the Myxophycean cell can be regarded 

 as an incipient nucleus is fairly clear, but it is not at all clear to what extent 



Fig. 7. A and B, the ends of two 

 tricbomes of Tolypotlirix lanata 

 (Desv.) Wartin., showing successive 

 stages of supposed mitosis. Fixed 

 in sulphurous acid and stained with 

 iron - ammonia - alum haprnatoxylin. 

 x 1160 (after Kohl). 



