DEVELOPMENT OF THE PERITHECIUM. I/ 



ultimate branching to form the ascogenous hyphae, the representation of 

 its exact form may be considered as a matter of secondary importance. 



With the first growth of the ascogonium in size the fusion nucleus 

 divides and we have a binucleated stage, which is apparently rather 

 long continued, lasting until the complete inclosure of the ascogonium 

 by the enveloping hyphae (figs. 13-16). It is an apparently abundant 

 stage and an easy one to study, since the fruits are now large enough 

 to be readily found, and the greater part of the ascogonium and the old 

 antheridial cell can frequently be found in a single section. The nuclei 

 are as a rule symmetrically placed in the axis of the ascogonium. In 

 Phyllactinia, according to my observations, cell division never follows 

 this first division of the egg-nucleus. The ascogonium remains one- 

 celled and its nuclei continue to divide. As to how many nuclear 

 divisions may precede cell division I am not certain, but in the end we 

 have formed a row of from 3 to 5 cells (figs. 17-22). The end cell of 

 the ascogonium regularly contains one nucleus and remains attached 

 to the old antheridial cell for a considerable period, though finally the 

 two are commonly forced apart, apparently by pressure of the surround- 

 ing cells of the enveloping hyphae. Sometimes this separation may 

 occur at quite an early period (fig. i8&). The old antheridial cell com- 

 monly remains at a depth of about two or three cell layers from the 

 surface of the perithecium, while the end of the ascogonium may 

 become more deeply buried by growth of the perithecial hyphae around 

 it. The ascogonium forms at its maturity a single row of cells, the 

 penultimate one of which regularly contains more than one nucleus. 



The next step in the development of the ascocarp consists in the 

 formation of the so-called ascogenous hyphae. These arise as lateral 

 branches from the ascogonium. Whether they all arise from a single 

 cell of the ascogonium, as one might expect from analogy with Asco- 

 bolus, or whether two or three of the upper cells may sprout out in 

 branches, is not easy to determine. It is certain that some branches 

 arise from the penultimate cell. The ascogenous hyphae arise relatively 

 early in the development of the ascocarp in Phyllactinia (figs. 22, 25a) 

 at a time when the ascogonium is inclosed by only about two layers of 

 perithecial cells. It is thus impossible for them to grow out vertically 

 from the ascogonium for any great distance, and the result is that they 

 lie flat on the cells of the ascogonium, crowding back the perithecial 

 cells and overlapping and intertwining with each other so as to cover 

 the whole upper part of the ascogonium. This makes it very difficult 

 to trace a particular branch to its point of origin, especially since the 

 walls of the cells are thin and their form distorted by the crowding of 



