180 proceedings of the american academy. 



Entomophtiiora. 

 Nucleus. 



The nucleus of E. Americana may be taken as typical of the genus. 

 The resting-nucleus varies in diameter from five to ten microns, with 

 an average of six. A successful stain gives a beautiful differentiation of 

 the nucleus and shows its structure in considerable detail (Figure 1). 

 The nuclear membrane is sharply defined, taking a much darker stain 

 than the rather faint gray-blue of the cytoplasm. Within the nucleus 

 there is a relatively small nucleolus, which stains red with the safranin- 

 gentian-violet combination. As a rule, the nucleolus is single, but in 

 some cases two or three may occur, when they are correspondingly 

 smaller (Figure 13), while in other cases the nucleolus may be altogether 

 absent (Figure 16). Around the nucleolus and occupying a large part 

 of the nuclear cavity occurs the chromatin, in the form of densely 

 packed granules. These usually appear evenly granular, but at times 

 this even appearance is much less marked, and the chromatin may 

 occur in the form of a fine meshed network (Figure 12). The chromatin 

 in the resting-nucleus stains deeply with the gentian-violet. 



The structure of this nucleus appears to be quite typical, and 

 certainly offers no support to the statement of Cavara (99) that " the 

 structure of these nuclei is quite singular, and perhaps has no counter- 

 part in those of any other plants, with the exception of the Saccharo- 

 mycetes . . . the nuclei of which recall very strongly those of the 

 Entomophthoreae." A comparison of the account of the nucleus of 

 the yeast given by Wager ('98), which is quoted by Cavara, with the 

 material of the present study fails to suggest the slightest similarity 

 in the two cases. Cavara further says, " It appears that the process 

 by which multiplication of the nuclei is effected must be ascribed to 

 division by fragmentation or to a modification of this which is tran- 

 sitional to mitotic division." The present study shows that the nu- 

 cleus of Entomophthora divides by a well-developed process of mitosis. 



The first indication of the approach of nuclear-division is to be 

 seen in the gradual loss of the dense, evenly granular condition of 

 the nucleus. The chromatin becomes less densely distributed, while the 

 granules are seen to be fewer and larger. This is followed by the 

 gathering of more and more of these granules in the central region of 

 the nucleus, which then shows a dense central mass of large chromatin- 

 granules surrounded by a clear area where a few scattered granules 

 occur, and linin-fibres are plainly visible (Figures 23, 24). Meanwhile 

 a change in staining-reaction has taken place, the granules retaining 



