IIO MARGARET C. FERGUSON 



plasm represents the last act of the egg in its preparation for 

 the reception of the sperm-nucleus. If it were formed by the 

 movement of nuclei or other bodies through the protoplasm, we 

 should expect the cytoplasm to draw together again, as during 

 the downward movement of the egg-nucleus ; but, in reality, 

 this opening persists throughout the entire later history of the 

 archegonium. Following fertilization it is sometimes found at 

 one side or a little below the neck of the archegonium. This 

 position is doubtless due to displacement at the time of con- 

 jugation (fig. 215). The regular clear outline of this cavity, 

 together with the fact of its presence in the unfertilized as well 

 as in the fecundated egg, warrants one in considering it a 

 definite character of the mature oosphere. 



I have suggested the name, receptive vacuole, for this vacu- 

 ole which is such a constant feature of the egg at the time of 

 fertilization and immediately prior to conjugation. The pollen- 

 tube suddenly empties into the archegonium a large amount of 

 material several nuclei, a comparatively large amount of 

 cytoplasm (see pollen-tube, fig. 120, plate XII, and fig. 214, 

 plate XIX) and considerable starch. The sudden acquisition of 

 this matter by an already densely filled egg might from the 

 increased pressure alone, cause fatal results. That the egg 

 should thus prepare for the reception of the sperm-cell is not 

 only a very beautiful, but a very interesting illustration of the 

 economy so often observed in nature. 



SUMMARY. 



After a period of growth the macrospore germinates and by 

 a typic division gives rise to the first two nuclei of the female 

 gametophyte. These usually pass to opposite poles of the pro- 

 thallial cavity and soon divide again. Divisions follow rather 

 leisurely during the fall, all the nuclei dividing synchronously. 

 After thirty-two or more free nuclei are formed the long period 

 of rest is entered upon. 



In early spring nuclear division is resumed and a large num- 

 ber of nuclei are formed ; about two thousand have been counted 

 at the time when cell-walls are first laid down. 



Walls are first developed in the prothallium during the latter 



