1022 AQUATIC PHYCOMYCETES 



oogonium the supporting hypha is drained of its contents. The mature 

 antheridium is hemispherical, with its broad face in contact with the 

 oogonial wall. It forms a blunt fertilization tube which pierces the 

 oogonium and which probably conveys into it the antheridial contents. 

 Minden evidently did not observe the actual process of fertilization. No 

 periplasmic material is discernible, and no contraction of the oogonial 

 contents occurs. After fertilization the droplets in the oogonium grad- 

 ually disappear, and coincidently a bright refractive "halo" becomes 

 visible on the periphery of the contents. This marks initiation of the 

 oospore wall. The hyaline material continues to replace the granular 

 contents until finally at maturity only a small spherical central part 

 composed of cytoplasm remains. The mature oospore consists, then, of 

 a small sphere of living contents, within which a conspicuous reserve 

 globule may frequently be observed, and an extremely thick hyaline, shin- 

 ing, concentrically layered wall, the outer surface of which is in close 

 contact, if not actually fused, with the wall of the oogonium (Fig. 88 H, 

 p. 1045). The mature oospores are usually formed within or near the sur- 

 face of the substratum and it is this fact together with the fragility of the 

 slender mycelium on which they are borne which makes it difficult in 

 gross culture to connect them with absolute certainty to the extramatrical 

 mycelium bearing the zoosporangia. 



The sex organs associated by Minden (1916) with Pythiogeton trans- 

 versum (Fig. 88 D) were similar in their general configuration to those 

 of P. utriforme, but differed in certain respects. The first divergence is in 

 the helical involvement of the supporting hyphae of the sex organs. 

 Whereas there can be seen in Minden's Plate 6, Figure 62, of P. utriforme 

 a slight tendency for the oogonial stalk to twist around that of the 

 antheridium, his description and figures of the sex organs of P. trans- 

 versum indicate that the oogonial hypha may make as many as four or 

 five turns around the supporting element of the male organ. Occasion- 

 ally the reserve situation was found. A second, even more striking, 

 difference concerns the external configuration of the mature oogonia 

 of the two species. This is spherical in P. utriforme but in P. transversum 

 it is distinctly polygonal, and the spherical oospore with its strikingly 

 thickened wall lies free within the oogonium. 



Stages in the germination of the oospore of Pythiogeton utriforme 



