538 



MOSSES AND FERNS 



CHAP. 



the leaf, the ligula. The spores are of two kinds, borne in sepa- 

 rate sporangia. The outer leaves of each cycle produce micro- 

 spores, the inner ones macrospores, many times larger than the 

 former. The innermost leaves, which are not usually perfectly 

 developed, are sterile, and separate one year's growth from the 

 next. In some of the land forms, e. g., I. hystrix, these sterile 

 leaves are very much reduced, and form spine-like structures. 



The Gametophyte 



The germination of the microspores was studied by Hof- 

 meister (i), and later by Millardet (i) and Belajeff (i), the 



Fig. 310. — A-G, Isoetes echinospora, var. Braunii. Development of the antheridium» 

 X about 1000. H, Spermatozoid of /. Malinverniana (H, after Belajeff). 



later writer differing in some essential particulars from the 

 earlier observers. The two former studied /. lacustris, the lat- 

 ter, /. setacea and I. Malinverniana, which do not seem to differ, 

 however, from /. echinospora, which was investigated by 

 the writer. The microspores of all the species are bilateral, and 

 are small bean-shaped cells with thick but in most species nearly 

 colourless walls. The epispore sometimes has spines upon it, 



