THE CELL 21 



nuclear spindle in Peziza vcsiculosa, an Ascomycete. The 

 presence of centre-spheres in the cells of animals has long 

 been known. In plants they have been observed chiefly in 

 cells concerned with reproduction, where they perform an 

 important function, inasmuch as the division of the nucleus 

 is determined by their influence in causing the separation 

 of the chromatin segments of a single nucleus into two 

 groups, each of which eventually becomes a nucleus. This 

 is effected by the two centrosomes, located at opposite ends 

 of the nucleus, repelling each other ; hence these bodies 

 have been termed kinetic centres or attraction spheres. In 

 a typical centrosphere there is a central differentiated 

 portion called the centrosome, and such structures have 

 been observed in connection with the division of nuclei in 

 the oosphere of Cystopus bliti by Stevens. This author 

 also states that in the species mentioned above, the sexual 

 nuclei differ in form, the male being elongated and the 

 female spherical. 



Chromosomes are formed by the fusion of the 

 chromatin-granules in the thread forming the nuclear 

 network. A reduction of chromosomes during nuclear 

 division has been observed by Stevens. 



Guilliermond has demonstrated that Dangeard's general- 

 isation, that the Ascomycetes have constantly four 

 chromosomes, is not correct. He observed eight in Peziza 

 cerea and in P. vesiculosa, twelve in P. cotinus, and sixteen 

 in P. rutilans. Trow points out that in Achlya de 

 Baryana, the reduction in the number of chromosomes, 

 from eight to four, takes place in the gameto-genesis, as in 

 most animals, and not in sporo-genesis, as in most plants. 



During the stage of nuclear division in the oosphere of 

 Cystopus candidus, Wager observed the appearance of a 



