62 



THE LOWER FUNGI— PHYCOMYCETES 



as doubtful members S. radicalis (Maire & Tison), S. verrucosa 

 (Maire & Tison), and S. isoetes (Palm). Further study may 

 result in the transfer of some of these latter forms to other genera. 

 A discussion of the doubtful genus Rhizomyxa Borzi (1884) 

 may be inserted most logically perhaps at this point. This 

 genus includes only the type species, R. hypogaea Borzi, 

 described as parasitic in the roots of a number of flowering plants. 

 It has been variously interpreted in the literature. Borzi 

 pictured and discussed both asexual and an asexual stage (Fig. 5), 



rTH f'l I 



Fig. 5. — Rhizomyxa hypogaea Borzi. (a) Young thalli in cortical cells of 

 Stellaria media, (h) Formation of sporangia, (c, d) Sori of sporangia, that 

 at (c) in a root hair, (e, f) Zoospores infecting host ceils, {g) Swarmspores. 

 {h) Germinating sporangia with exit tubes, (s) Thallus divided by septum 

 to form oogonium and antheridium. (0 After fertilization showing oospore 

 in oogonium. {After Borzi I884.) 



but in the light of later work on other forms it seems highly prob- 

 able that he based his description on a mixture of two or more 

 different organisms. In the sexual process as described the 

 thallus elongates and becomes septate into two unequal cells, 

 one of which functions as an antheridium and the other as an 

 oogonium. In the oogonium a differentiation of the contents 

 into periplasm and ooplasm precedes fertilization, and at matur- 

 ity a single oospore lies free in the oogonium. This account was 

 accepted by Schroter (1892: 91) and he was led by it to place 

 the genus in the Ancylistales. Fischer (1892: 69), von Minden 

 (1911: 278), and others have excluded this stage from consider- 

 ation. In the asexual phase, according to Borzi, the thallus is 



