W. Kobinson i:>l 



swollen bodies is densely filled with protoplasm, contains several 

 nuclei and also large numbers of the deeply staining granules already 

 referred to (Fig. 8). Up to this point, however, no septum has appeared 

 below the swollen portion. The apex of each body becomes very 

 closely pressed against the cuticle and then penetrates the latter by a 

 fine hypha which at once grows out to produce sporangia. The out- 

 growing hypha may branch at the point of exit (Fig. 9) and produce 

 several sporangiophores or merely give rise to one. Frequently only 

 a single terminal sporangium is borne upon such a sporangiophore, 

 but in many instances series of three or four sporangia arise successively 

 in a sympodial manner. This mode of production of the sporangia 

 is characteristic of several species of Phytophthora. 



The sporangium arises as a slight swelling of the tip of the hypha 

 bearing it, and this swelling gradually enlarges, becoming first globular 

 and then oval in shape (Fig. 10 a, b, c). At maturity it measures on 

 an average 32/z by 60fx, being then separated from the hypha bearing 

 it by a transverse septum. The apex of the sporangium does not 

 always show a very definite papilla as in other species of Phytophthora. 

 As it approaches maturity a large central vacuole appears (Fig. 12) 

 and this corresponds in position and appearance to the central oil 

 body described by Pethybridge 1 in Ph. erythroseptica. A little before 

 maturity the vacuole disappears and then the contents of the sporangium 

 are seen to have divided up into 13 to 15 zoospores (Figs. 13, 14, 15). 

 The sporangia germinate while still attached to the stalk and have 

 never been observed to fall off as in Ph. infestans. Germination of the 

 sporangia may take place either by the liberation of motile zoospores 

 (Fig. 18) or under different conditions by the direct production of a 

 germ tube (Fig. 17). This corresponds to the observations of De Bary 2 

 and of more recent investigators on different species of Phytophthora. 



Reference has already been made to the method by which the 

 liberation of zoospores was observed. The discharge takes place imme- 

 diately on transferring ripe sporangia into fresh well-aerated tap water. 

 It is brought about by the solution or the opening of the apical portion 

 of the sporangium, and a vesicular swelling-out of the apex has never 

 been observed. The zoospores mature within the sporangium and are 

 directly discharged in a mass, in groups of two or three or one after 

 another. As has been observed by many investigators in other species 

 of Phytophthora, some of the zoospores occasionally fail to be discharged 



1 loc. cit. 2 loc. cit. 



# 9—2 



