92 



PLANT MORPHOLOGY 



carpogonium (Fig. 79.4, B). The nucleus of the carpogonium divides 

 into two nuclei, one of which passes into the trichogyne and finally dis- 

 integrates, while the other remains in the carpogonium and functions as 

 an egg nucleus. The pericentral cell also gives rise to a group of auxiliary 

 cells, one of which crowds in between the pericentral cell and the carpo- 

 gonium (Fig. 79C). The entire structure comprises the procarp. 



The free-floating spermatium, coming in contact with the trichogyne, 

 remains uninucleate. The male nucleus enters the trichogyne, passes 



Fig. 79. Diagrams showing development of procarp of PoJysiphonia. A, early stage: 

 B, later stage, the pericentral cell (p) having produced four cells, the terminal one forming 

 the carpogonium (c) and trichogyne (0 ; C, mature stage, a group of auxiliary cells having 

 developed from the pericentral cell. (After Yamanouchi.) 



into the carpogonium, and fuses with the female nucleus. A passageway 

 to the pericentral cell now is opened through the intervening auxiliary 

 cell and the fusion nucleus passes through. Then all the cells of the 

 procarp unite and the fusion nucleus divides to form many nuclei. Lobes 

 into which these nuclei pass are put out from the procarp and then the 

 carpospores are cut off. The whole structure comprises the cystocarp 

 (Fig. 77C). The usual envelope of sterile cells is formed around it. 



After escaping from the cystocarp, a carpospore gives rise to a tetra- 

 sporic plant. A stalked sporangium is produced laterally from an axial 

 cell, pushing through the cortical cells. The tetraspores give rise to 

 sexual plants. Polysi'phonia displays an isomorphic alternation of 

 generations. The sexual plants, with haploid cells, are gametophytes. 

 The tetrasporic plant, with diploid cells, is a sporophyte. The sporophyte 

 generation, however, beginning with the zygote, includes also the cysto- 



