SPECIAL NUCLEAR PHENOMENA. 3 1 



ordinary hyphal nuclei. The nuclei of the stalk cells of both oogonium 

 and antheridium, from which the protective hyphae are to sprout, are 

 frequently larger (figs. 7, 10), at least at the stages when the formation 

 of the perithecium is about to begin, than those of the ordinary hyphal 

 cells, though not as large as the nucleus of the oogonium. As in many 

 other cases, the male nucleus is regularly smaller than that of the egg, 

 just as the antheridium is smaller than the oogonium (figs. 5, 6, 7, 8, 9). 

 After fertilization, with the growth of the ascogonium its nuclei 

 become still larger, and in the young ascus the pair of nuclei which fuse 

 are conspicuously larger than any that have preceded them (figs. 31-33), 

 and the product of their union, the primary nucleus of the ascus, is one 

 of the largest nuclei to be found among the fungi (figs. 48, 49). It is 

 much larger than the nuclei of the cells of the leaf on which the mildew 

 grows. Its diameter is about 10 /:* as compared with a diameter oi 2 /t. 

 in the hyphal nuclei. This large size of the primary nucleus of the 

 ascus may well be regarded as correlated with the large size of the ascus 

 itself. Roughly, the volume of the nucleus of the ascus seems to stand 

 in a similar proportion to the volume of the entire ascus as the volume 

 of a hyphal nucleus does to the cell which contains it. The cells of the 

 full-grown perithecium contain several nuclei which are rather smaller 

 than those of the mycelial cells, which are regularly uninucleated. 

 When the primary nucleus of the ascus divides, the daughter nuclei are 

 certainly not more than half as large (fig. 62) as the parent nucleus. 

 The size of the nuclei produced in the second and third divisions is also 

 proportionally reduced, and finally the nuclei of the ascospores are of 

 about the size of the ordinary nuclei of the young perithecium (fig. 79) . 

 There can be no doubt that we have here a definite correlation between 

 nuclear and cytoplasmic masses, such that the larger cells contain 

 proportionally larger nuclei, and we have thus an illustration of the 

 principle of the nucleo-cytoplasmic relation developed by R. Hertwig, 

 GerassimoflF, and Boveri. 



The nucleus of the oogonium is, as noted, considerably larger than 

 those of the vegetative hyphae. The oogonial cytoplasm is quite dense 

 and shows a fine, close, spongy structure (figs. 1-7). The central body 

 of the oogonial nucleus is a conspicuous, well-differentiated, disk-shaped 

 granule (figs. 4, 5, 7) lying close on the surface of the nuclear mem- 

 brane and generally occupying a slight depression in it. The arrange- 

 ment of the chromatin content of the nucleus can not be so clearly made 

 out at this stage as at later stages in the larger nuclei of the ascogenous 

 hyphse and the asci ; still it is perfectly plain, in every case in which the 

 plane of the section permits a profile view of the structure, that the 



