554 Scientific Proceedings, Royal Dublin Society. 



description (4, 5) and figures of the sexual organs of this species the close 

 resemhlance between them and those of P. erythroseptica was at once evident. 

 Moreover, the following sentence was found to occur in Clinton's descrip- 

 tion: — "For a long time it was difficult to decide whether or not these 

 [oogonial] threads did not actually penetrate the antheridium and grow 

 through it, and we are not yet certain that this does not sometimes occur. 

 Certainly the optical effect is frequently tliat of an internal thread with its 

 apical walls very thin as compared with the side walls . . . " Further 

 on he writes, " If the oogonial thread really ever penetrates the antheridium, 

 a union of certain of their protoplasmic contents no doubt takes place at that 

 time." 



Lima-bean-agar, the medium on which P. PhaneoK grew best with me, is 

 also semi-opaque and unsuitable for cover-glass film cultures, and I have been 

 unable to trace in continuity the development of the sexual organs in this 

 species. From what I have seen of them, however, in preparations made from 

 cultures on Lima-bean-agar in test-tubes, I have no hesitation in describing 

 them as being of the same type as those of P. infestans and P. erythroseptica. 



Fig. 23, Plate XLIV, is drawn from one of these preparations, and the 

 oogonium here is clearly a pear-shaped structure with its lower end within 

 the antheridium. The depression in the antheridium wall at the point where 

 the oogonial incept entered is clearly marked. 



Possibly P. Thalictri may belong to the same type. From Clinton's (4) 

 description of this fungus it appears, as regards its vegetative characters and 

 its asexual mode of reproduction, to resemble P. infestans closely. The 

 oospores are stated not to differ materially from those of P. Phaseoli ; but 

 since they were only obtained with difficulty, and after macerating an affected 

 leaf in boiling caustic potash solution, there was little hope of seeing the 

 relationship of the antheridia (if present) to the oogonia. 



Considering next tlie case of Phytophthora omnivora var. Arecae Coleman 

 (7), which causes a disease of the Areca palm in India, the author of this 

 variety says of it : " The formation of the oogonia and the antheridia 

 followed quite closely that of Phytophthora omnivora so carefully described by 

 de Bary." An examination of the figures of these organs which Coleman 

 published with his paper suggests to me strongly that this is not really the 

 case. One of these figures is reproduced (on a reduced scale) in Plate XLIV, 

 fig. 24, and the striking general similarity between it and the figures given 

 for P. erythro&eptica, P. infestans, and P. PhaseoU will at once be noticed. 

 All that appears to be lacking is the hypha bearing the antheridium. In all 

 the twelve figures published by Coleman of the sexual organs of tlie Areca 

 Phytophthora (except one in which the antheridium is not shown) the 



