LEPTO MIT ALES 859 



fertilization tube. The wall of the oospore is generally roughened or 

 ornamented, presumably by periplasmic material. 



The oogonia originate singly or in whorls in the same manner as the 

 zoosporangia. They are frequently distinguishable from the latter, 

 however, by their more spherical shape. A constriction is always present 

 beneath the oogonium which divides it from its concomitant hypha. 

 After the oogonium has received its complement of protoplasm and 

 nuclei from the thallus it is separated by a plug of wall material. Details 

 of the protoplasmic changes which then occur are discussed under 

 "Cytology" (p. 861). The antheridium in some species is monoclinous; 

 in others, diclinous. It is borne at the tip of a more or less extended 

 slender branch, and its broad apex is applied to a well-defined spot on 

 the oogonial wall. A cross wail separates the expanded antheridium 

 from the slender sometimes branching hypha which bears it. The 

 oospore proper never completely fills the oogonium. It has an inner 

 smooth wall of moderate thickness and an outer one derived from the 

 periplasm. In Rhipidium (Fig. 71 C, p. 894) this outer wall is folded into 

 a series of anastomosing ridges which give it an irregular stellate appear- 

 ance, whereas in Sapromyces (Fig. 70 B, p. 890) the wall is almost but 

 not completely smooth, the degree of undulation differing with the 

 species. The oospores of Araiospora (Fig. 70 D, G) are striking objects. 

 Here the living contents, bearing one or more brilliantly golden globules, 

 are surrounded by a thick smooth wall, which in turn is enveloped by a 

 single layer of thin-walled hexagonal cells. Germination of the oospores 

 has not been observed in any member of the family. 



An interesting series of investigations of sexuality in one of the 

 Rhipidiaceae, Sapromyces elongatus, was carried on by Jordan (in 

 Weston, 1938) and Bishop (1940). The almost complete agreement 

 among the relatively few observers of this species that its antheridia 

 were diclinous in origin (Fig. 70 B) naturally raised the question as to 

 whether or not it was actually heterothallic in the sense in which that 

 term had been applied to the Mucorales (Blakeslee, 1904). Preliminary 

 studies by Jordan on single isolated basal cells of either oogonial or 

 antheridial plants showed that when these were transplanted to sterile 

 water cultures baited appropriately and grown alone no sex organs 

 were produced. There was, however, one exception, a female strain which 



