SAPROLEGN 1 ALES 177 



prominent cellulin plug. The oogonial wall is characteristically 

 encrusted with a dark-colored flaky material. The antherid- 

 ial branches are characteristically twisted. In *S. reinschii 

 (Schroter) Fritsch they are diclinous being long and winding, 

 in S. androgynous Thaxter (Fig. 66) they are androgynous and 

 short. These two species constitute the genus. The antherid- 

 ium is terminal, and sends a fertilization tube to the solitary 

 spherical oosphere. 



4. Araiospora Thaxter (1896: 326). 



In Araiospora the thallus is definitely tree-like (Fig. 67). A 

 prominent cyhndrical trunk of broad diameter is attached to 

 the substratum by rhizoids, and bears at its apex a number of 

 relatively slender cylindrical branches which in turn branch 

 repeatedly in a definitely umbellate fashion. The branches are 

 constricted at intervals, the secondary branches arising at the 

 distal end of the segment. Two types of sporangia are formed, 

 one smooth, the other more or less ornamented with spines or 

 finger-like processes. The two differ also somewhat in shape 

 and size, the smooth type tending to appear first and being the 

 more slender. The genus at present contains three species, 

 A. pulchra Thaxter, A. spinosa (Cornu) Thaxter, and A. coronnta 

 Linder (1926: 176). In the first two species the second type of 

 sporangium is barbed over its surface with sharp spines. In 

 A. coronata it is provided merely with a crown of finger-like 

 processes at its apical end, and has somewhat the aspect of a 

 basidium. Zoospore emergence occurs as in the preceding genus, 

 a thin-walled vesicle being sometimes formed at the mouth of 

 the sporangium and existing for a brief period. Oogonia and 

 sporangia are often found associated, and both occur in whorls or 

 umbels. They are separated from the hyphal segment by a 

 definite constriction. The oogonium is spherical and mono- 

 sporic. At maturity the oospore is surrounded by a layer of 

 cell-like compartments which gives it a very characteristic aspect. 

 Antheridal branches arise from special segments and may be 

 branched. The antheridium is apphed near the base of the 

 oogonium. King (1903) studied A. pulchra in stained prepara- 

 tions and describes fertihzation of a uninucleate oosphere as 

 resulting from the entrance of a single antheridial nucleus. The 

 genus is considered taxonomically by von Minden (1912: 588) 

 and Kanouse (1927:345). 



