Pkthybridge — Observations on PhytopMhora erythroseptica. 181 



in respect of one detail, namely that, according to Dastur, in this species 

 the oogonial incept (" origin " of Dastur) may arise on the same hypha as the 

 antheridium, and indeed may arise from the base of the autheridium itself as 

 an ingrowth. Butler, however, states that in P. Colocasiae " so far as could 

 be determined the oogonium arises always from a different hypha from that 

 which bears the antheridium. Sometimes, however, the stalks of both organs 

 swell up, and a tangled mass results, which prevents their origin being 

 ascertained." The same holds good more or less for P. evythroseptica ; and 

 antheridia and oogonia have so far never been seen other than on separate 

 hyphae. 



Although the development of the sexual organs follows essentially the 

 same course in the three species mentioned tliere are in certain details of these 

 organs, as well as in other characters, considerable morphological differences 

 between them, and the three species are by no means to be regarded as 

 identical. 



In the paper on P. erythroseptica already published some important 

 points in the character and behaviour of the fungus were not fully described, 

 as they had at that time been but partially elucidated. 



These points relate chiefly to : — 



(1) The micro-chemical reactions of the walls and the mode of 



germination of the conidia (zoosporangia). 



(2) The micro-chemical reactions of the walls of the sexual organs 



and the germination of the oospores. 



(3) The occurrence of the fungus in parts of the potato plant 



other than the tubers (in which it had been found merely in 

 its vegetative condition), and the occurrence in such parts of 

 its sexual and asexual reproductive organs which hitherto had 

 only been observed when it was grown as a saprophyte in pure 

 culture on artificial media. 



It is the object of the present paper to furnisli information on these 

 matters obtained frona further researches carried out during the past season. 



I desire to express to Mr. H. A. Lafferty, a.h.c.sc.i., a Research Scholar 

 of the Royal College of Science for Ireland, who has been working in my 

 laboratories for the past twelve months, my indebtedness for much assistance 

 rendered in various ways (including the preparation of the drawings for text 

 figs. 1 and 2) during the progress of the work the results of which form the 

 basis of the present paper. 



2 E 2 



