BLASTOCLADIALES 131 



hypha may cause it to assume a lateral position. Less often 

 sporangia are cut off in basipetal succession, and form a chain 

 (Coker and Braxton, 1926: pi. 10). The swarmspores are mono- 

 planetic. In some cases they pass into a vesicle as in Pythium 

 before being freed. In Gonapodya repeated proliferation of new 

 sporangia within the old occurs. 



The resting sporangium is an outstanding feature of the 

 morphology of Blastocladia and Allomyces, but is absent in Gona- 

 podya. It corresponds more or less in form, size, and position 

 with the thin-walled sporangium, but is clearly very different 

 in character. It is thick- walled, the wall being composed of 

 three layers, a middle thick layer and outer and inner thin ones. 

 The outer layer is in reality the original wall of the hyphal cell, 

 and in some species at the maturity of the resting sporangium 

 this outer wall splits allowing the sporangium, enclosed in the 

 other two walls, to fall away. In other cases the outer wall 

 remains in close contact with the sporangium and is carried away 

 with it. The appearance of the mature resting sporangium is 

 characteristic. In no other known group of Phycomycetes 

 is there a similar structure. Its surface is covered with minute 

 dots, which are shown in section to be the mouths of cyhndric 

 tubes lying in the middle wall and almost traversing it. At 

 germination this wall cracks open, and a prominent exit papilla 

 is formed on the inner, the escaping swarmspores resembling 

 those freed by the thin-walled sporangium. 



Various names have been applied by different writers to this 

 resting sporangium. It has been termed the conidium, the 

 resting spore, and the resting cell. Butler (1911: 1030) suggests 

 that it is perhaps a parthenogenetic oospore. Kanouse (1927: 

 292) uses the terms oogonium and oospore in this connection 

 without quaUfication. Moreover, she describes and figures for 

 Blastocladia glohosa Kanouse, slender filaments associated with the 

 resting sporangium which, she says, are undoubtedly antheridial 

 branches. In a single case, she found a cell cut off at the tip of a 

 branch by a definite septum, and regards this as an antheridium. 

 The process of fertiUzation was not observed, nor, in fact, any 

 indication given as to how it may be effected. She suggests 

 the possibility that it is accompHshed by means of motile male 

 cells, though none were observed. She admits that, in any case, 

 these so-called "antheridia" are rare, and that the "oospores" 

 (parthenospores) usually mature parthenogenetically. 



