t 



1907] 



PFEIFFER—SPOROCARPS IN AZOLLA 



447 



In 1898 GoEBEL (5) again investigated the method of sporocarp 

 development in A. filiculoides. He accepted Strasburger's later 

 account of the development of the microsporocarp, but in the mcga- 

 sporocarp he found in the later stages of development primordia of 

 microsporangia which had aborted. 



In Campbell's revised edition of Mosses and / 



1905)' 



he refers to Goebel's account and states that "in the microsporangial 

 sorus the apex of the receptacle, which probably represents an abor- 

 tive macrosporangium, forms a columella, from whose base the 



microsporo 



microsporangia develop." He uses the illustration of the 



carp which he had used in the origina] paper, and shows the columella 



as a club-shaped body which has little resemblance to a sporangium. 



INVESTIGATION 



I 



Working on Azolla caroliniana, I have traced the development 

 of the sporocarp, paying particular attention to the stage at which 

 microsporocarp and megasporocarp are definitely differentiated. 



The youngest stage in which the sporocarp can be readily recog- 

 nized shows a young sporangium consisting merely of an apical cell 

 and a short stalk, about whose base there is a ringlike projection 

 (fig' i"). This sporangium, which holds the central position in the 

 mature sporocarp, is the mcgasporangium, and is of the ordinary 

 leptosporangiate type. 



The projecting ring of cells about the base of the sporangium, by 

 subsequent growth outward and upward, forms the wall of the sporo- 

 carp. Growth of the sporangium and growth of the sporocarp wall 

 go on simultaneously, so that by the time the primary tapetal cells 

 are cut off in the capsule of the sporangium, the two-layered 

 sporocarp wall stands almost as high as the sporangium {fig. j). 

 While the development of the capsule of the sporangium has 



way, there has been no 



gone on in the regular leptosporangiate 



pedicel as might be expected. 



The 



such elongation of the 



divisions of the cells of the pedicel, for the most part, have 

 been anticlinal rather than periclinal to the apical cell, so that 

 the stalk is massive, almost as great in diameter as is the capsule 

 ifiS' 3)' Growth in the capsule now continues in the usual way 

 until there is finally a sporangium having one layer of wall cells 



J, 



! 



