in 



THE JUNGERMANNIALES 



83 



California (Campbell (18)). Geothallus tuber osus (Figs. 

 34, 35), differs from Sphcerocarpus in its much larger size, 

 the development of leaf-like organs, much like those of Fos- 

 somhronia and by the very much larger size of the spores. 

 There are also some minor differences in the structure of the 

 reproductive organs, the antheridia having a more massive 

 pedicel than that of Sphcerocarpus. The plants are perennial, 

 and at the end of the growing season the younger parts of the 

 thallus become changed into a tuber with a thick black cover- 

 ing. The tubers are buried in the earth during the dry season. 



-n. 



Fig. 35. — Geothallus tuberosus. A, Archegonium, X200; B, ripe antheridium, X about 

 65; C, a four-celled embryo, X200: D, ripe spore; E, sterile cells. Xioo. 



The apex of the shoot persists and resumes growth as soon 

 as the conditions are favorable. 



Riella. 



The peculiar genus Riella (Goebel (17), Leitgeb (7), Por- 

 sild ( I ) ) , while it closely resembles Sphcerocarpus in the struc- 

 ture of the reproductive organs and sporophyte, differs very 

 much in the habit of the gametophyte. Until very recently 

 (Howe and Underwood (3)), all the species known were 

 from the regions adjacent to the Mediterranean, but one species 

 has since been found in the Canary Islands, and another in the 

 United States. They are all submersed aquatics. The thal- 

 lus shows a cylindrical axis, from which grows a thin vertical 



