94: THE SAPEOLEGNIACE^ OF THE UNITED STATES, 



the very end of the tube after the wall of the oospore has become thick and dense 

 (Fig. 34, a). Since it is impossible to accept any view of fertilization which does 

 not involve the passage of a nucleus from the tube, these facts must remove all pos- 

 sible doubt of the correctness of the belief expressed by DeBary that these fungi are 

 no longer truly sexual, in spite of their fully developed sexual organs. 



After the thickening of its wall, a period of a few days is necessary for the com- 

 plete ripening of the oospore. The visible sign of this process lies in the separation 

 of the fatty material, which has been until now scattered in small globules through 

 the protoplasm, into one or a few large and more or less spherical masses. While in 

 certain species it characteristically remains in several portions (Fig. 6S), it is com- 

 monly fused into a single drop (Fig. 111). This generally continues surrounded by 

 protoplasm and nearly central (Figs. 95, 111), although it may be so much displaced 

 as to leave only a thin film of protoplasm over one side. Oospores of this type are 

 called centric, to distinguish them from those of excentric structure, in which the oil 

 globule or globules and the protoplasmic mass occupy opposite sides of the spore, 

 and are in contact only by their margins (Figs. 68, 73). 



After a period of rest which varies greatly in different species, the oospores may 

 germinate. Preparation for this process consists in the breaking up of the oil glob- 

 ule and its rediffusion through the protoplasm. The inner membrane of the spore 

 no v/ grows out through a rupture in the outer one into a short thread similar in 

 estructure to a vegetative hypha (Fig. 29, a). If this thread comes at once into con- 

 tact with available nourishment, it may develop rhizoids and branch, and so grow 

 directly into a new plant. But if nourishment be not immediately at hand, the hypha, 

 after a brief growth, forms a sporangium at its apex in the manner typical of its 

 genus. There can be no doubt that the numerous nuclei of the germ-hypha arise 

 from the division of the single nucleus of the oospore, but how early the division 

 begins is not certain. Dangeard ('90) maintains that the oospores are always multi- 

 nucleate, and it may be that this division begins, at least in some species, quite early, 

 and that therefore he has overlooked the uninucleate stage. He suggests that a dif- 

 ference may be found between oospores which germinate at once and those which 

 require a considerable period of rest. But there is no doubt that the oospores of A. 

 apiculata, which, according to DeBary ('84), germinate as soon as they are ripe, are 

 distinctlv uninucleate. 



In comparing the chlamydospores and the oogonia of the Saprolegniacem, we may 

 assume what is probably true, that no nuclear changes occur within the former. If 



