1907] PFEIFFER—SPOROCARPS IN AZOLLA 



449 



become almost if not com 



of the cells of the outer layer. The general shape of the sporocarp is 

 oval, flattened on one side, and with a beak of enlarged cells at the 

 top. Just inside this wall one often finds unattached filaments of 



Anabaena 



At the 



massive 



Of these sporangia, the oldest, which holds the central position, is 

 the megasporangium, while the very young microsporangia form 

 one or more whorls about its base. Within the mesasporangium 



mass 



small 



in the center, surrounded by the most densely granular of this cyto- 



m 



Ihe question now is whether the megasporangium or the group 

 of microsporangia, all of which are apparently vigorous, shall go on 

 developing. If the megasporangium develops, there will be a mega- 

 sporocarp; while if the microsporangia develop, there will be a micro- 

 sporocarp. 



In the megasporocarp, "thirty-one of the megaspores abort, while 

 one, which usually holds the central position in the sporangium, 

 continues growth {jig. g). The megasporangium increases in size, 

 but there is no further elongation of the stalk, and the young micro- 

 sporangia at its base cease their growth. As the megasporangium 

 increases in size, it finally completely fills the sporocarp, and the 

 young microsporangia are squeezed down against the stalk until they 

 are hardly recognizable. An abnormal condition, which I found 



me 



while only thirty abort. 



mega spore 



abortion of the spores "in the megaspo- 

 tian in the megasporocarp, and we find 



all thirty-two megaspores aborting. Within the megasporangium 



asm 



masses, and the me 



hang together in tetrads or may fall apart as separate spores, are 

 shrunken and shapeless (fig. 10). As this abortion goes on, the 

 stalk of the megasporangium elongates somewhat and new microspo- 

 rangial primordia continue to appear below the older ones, which are 



