DEVELOPMENT OF THE PERITHECIUM. II 



nuclei. Figs. 5, 6, and 7 show successive stages after the gametes have 

 been differentiated and just before fertiHzation occurs. The oogonium 

 especially grows in size, and both the egg and male nuclei also increase 

 in size. At the time of fertilization the male nucleus is smaller than 

 the egg-nucleus, but hardly, perhaps, to the same degree that the anther- 

 idial cell is smaller than the oogonium. The cytoplasm of both gametes 

 is quite free from reserve food granules or other stainable inclusions at 

 this stage. Some small bodies, staining red with the triple stain, and 

 a good many small spherical vacuoles are present in the oogonium, as 

 shown in the figures, but for the most part the cytoplasm is a fine- 

 meshed, spongy mass, which appears pale-bluish or gray with the triple 

 stain. The nuclei are very sharply and characteristically differentiated 

 at this stage, and their structure will be described in detail later. The 

 antheridium is closely pressed upon the oogonium a little to one side of 

 and generally above the apex of the latter. Their walls in the region 

 of contact are flattened upon each other and closely united. Every 

 appearance is similar to those found in other cases of non-motile conju- 

 gating cells among the algae and fungi. 



A portion of the walls between the antheridium and the oogonium 

 is now dissolved in such a fashion as to form a circular conjugation- 

 pore leading from the antheridium to the oogonium. The protoplasts 

 of the antheridial and oogonial cells are thus brought into direct contact 

 and combine to form a continuous protoplasmic mass (figs. 8, 9). The 

 nucleus of the antheridium migrates through the conjugation-pore into 

 the oogonium and approaches the egg-nucleus. The male nucleus, is, 

 at this stage also, somewhat smaller than the egg-nucleus. This inequal- 

 ity in size is, however, by no means so great as is found in the pronuclei 

 of many other plants and animals, in the early stages of the process 

 of fertilization. Figs. 8 and 9 show cases in which the conjugation- 

 pore is open 'and the male and female nuclei are side by side in the 

 oogonium. In fig. 9 the male nucleus, as recognized by its smaller size, 

 has moved past and appears on the side of the egg-nucleus farthest from 

 the antheridium. 



It is evident that the conjugation-pore can be most easily found 

 and studied in cases in which the plane of contact of the antheridium 

 and oogonium cut the plane of the section at right angles, or nearly so, 

 as is the case in figs. 9, 10, and 11. Cases in which the sexual cells 

 present the aspects shown in figs. 6 and 7, in which the antheridium is 

 more or less behind the tip of the oogonium, are of course much less 

 favorable for the discovery and study of the actual fusion of the cells. 

 Still it is perfectly possible in well-fixed and clearly stained material to 



