DEVELOPMENT OF THE PERITIIECIUM. 15 



base of the perithecium considerably to one side of its stalk and com- 

 monly in about the third layer of cells from the surface of the perithe- 

 cial wall. From the time of the completion of the process of fertilization 

 and the closure of the conjugation-pore it is most conspicuously a dead 

 cell, and its differentiation from all the later-formed perithecial protect- 

 ive cells, both in function, structure, and fate, is one of the most con- 

 spicuous facts that appears in any series of sections of the developing 

 ascocarp of Phyllactinia, and is in itself sufficient to suggest the mor- 

 phological relationships of the ascocarp. 



The fertilized oogonium in Phyllactinia begins its further devel- 

 opment at once. The egg in this case is the oogonium, and the use of 

 the term oosphere seems quite superfluous. We have no rounding up 

 of the protoplast of the oogonium and separation from its wall to form 

 an oosphere, as in Oedogonium or Vaucheria. Still, there is no ques- 

 tion that the female cell in Phyllactinia corresponds entirely to that of 

 Oedogonium ; and the fact that it does not round itself up is due to its 

 habit of continued development as a cell of the mycelium which pro- 

 duced it. It is set free from vegetative continuity with the mother 

 plant in no respect. Whether it is to be regarded as the beginning of 

 a new individual life history is a question which must be settled on 

 other grounds than that of its being set free from the mother plant as 

 an independent life unit. 



While the process of fertilization is going on, the protective branches 

 which are to form the perithecial envelope push out from the stalk-cell 

 of the oogonium and grow up about the two gametephores, applying 

 themselves closely to their surface and following an irregular path, 

 owing to the slight spiral twisting of the oogonium. In the figures I 

 have put in only such portions of them as lay outside the outlines of the 

 sexual apparatus. In Phyllactinia it is very conspicuous that these 

 enveloping branches may and do arise from the stalk-cell of the anther- 

 idium as well as from that of the oogonium (figs. 14, 17). Even 

 before fertilization is complete the antheridial stalk-cell becomes much 

 enlarged and is apparently in a very active vegetative condition (fig. 7), 

 resembling that of the stalk-cell of the oogonium. After fertilization 

 its condition is in striking contrast with that of the antheridial cell which 

 was cut off from it. While the walls of the latter swell and apparently 

 become mucilaginous, and its protoplast degenerates as described above, 

 the stalk-cell continues to enlarge, its nucleus divides, and hyphal buds 

 push out from its surface At the very first one or more hyphal branches 

 push out just below the cross-wall separating the antheridium from the 

 stalk-cell and grow up over the former (fig. 14), inclosing and covering 



