870 AQUATIC PHYCOMYCETES 



A receptive papilla is formed from a differentiated portion of the egg, 

 just within the oogonial wall at the point of application of the antherid- 

 ium. A fertilization tube is produced which King considers to be laid 

 down by periplasmic material, not by the antheridium. This point is 

 contrary to Thaxter's observations on living plants of Araiospora pulchra 

 and Kevorkian's (1934) with respect to a congeneric form, A. strep- 

 tandra. Behrens, too, concludes from his cytological study of Rhipidium 

 interruptum that King was in error, and shows that the fertilization tube 

 in Rhipidium, after its tip has deliquesced, gives the appearance of being 

 a canal of oogonial origin. The antheridium contains from five to seven 

 nuclei. From the fact that the older antheridia contained twice this 

 number, it was presumed that here, as in the oogonial nuclei, a mitotic 

 division had occurred. At fertilization a single nucleus is introduced 

 into the egg; the remainder degenerate. While the two sexual nuclei 

 approach the center of the egg (and each other) they become beaked, 

 as though a mutual attraction existed between them. No nuclear fusion 

 was found, and wholly mature oospores were always binucleate. Like 

 Behrens, King suggests that karyogamy probably occurs at the close of 

 the rest period undergone by the oospore. 



During the maturation of the oospore the nuclei increase in size. If, 

 as is usual, a large central reserve globule is formed, they are displaced 

 laterally. Although the point is not clearly brought out by King there 

 is much evidence in the figures given to indicate that in Araiospora 

 pulchra the wall of the oospore proper is formed in much the same 

 manner as was described by Behrens for Rhipidium. The cellular enve- 

 lope, so characteristic of Araiospora (Fig. 70 D, F-G, p. 890) but not 

 found in Rhipidium, appears to be formed directly from the periplasm. 



Physiology 



Precise knowledge of the metabolic processes and conditions neces- 

 sary for growth in members of the order is confined chiefly to two 

 genera of the Leptomitaceae, Leptomitus and Apodachlya. Schade (1940) 

 and Schade and Thimann (1940) made comparative physiological inves- 

 tigations of L. lacteus and A. hrachynema. The more extensive literature 

 pertinent to the physiology of Leptomitus is cited in their papers. Find- 



