196 Scientific Proceedings, Royal Dublin Society. 



potatoes for five years in succession, over twelve per cent, of the total yield of 

 tubers vfas destroyed by this disease. On similar land two years in potatoes 

 the loss was nearly four per cent., whereas on fresh land of the same 

 character the loss was only 0'03 per cent. 



It is obvious, therefore, that it takes some years for land to become 

 contaminated to an extent sufficient to cause very serious losses; and if a proper 

 rotation be followed, such losses are practically negligible. 



Since the soil must become contaminated from the resting-spores present 

 in the decayed portions of the plants, it is clear that collecting and burning 

 the potato haulms previous to digging is a practice strongly to be commended ; 

 for if this be done, there is less chance of other areas becoming contaminated 

 through such dibris as might reach it via the manure-heap or in some other 

 way. Furtlier, it would be prudent to destroy or bury deeply all affected 

 tubers when lifted, seeing that they too may possibly harbour the resting-, 

 spores of the fungus. 



SUMMARY. 



The present paper contains further observations on F hytophthora erythro- 

 septica Pethyb., which in a former one was shown to be the cause of a 

 specific rot (" Pink Rot ") of the potato tuber. 



Attention is directed to the fact that the peculiar mode of development of 

 the sexual organs described for this fungus, and shown to occur also in 

 P. infestans de Bary, P. Phaseoli Thaxt., has also been observed independently 

 in P. jMrasitica n. sp. and P. Colocasiae Racib. by Dastur and by Butler and 

 Kulkarni respectively. This brings up the total number of species in the 

 genus Phytophthora, as restricted by the present author, to five certain species 

 with a possible sixth, viz., P. omnivora var. Arecae Coleman. 



The microchemical reactions of the walls of the hyphae, conidia, and . 

 sexual organs show that these are largely but not entirely composed of 

 cellulose. The walls of the oogonium and of the oospore each consist of two 

 layers, the thin, outer portions being coloured yellow with iodine reagents, and 

 not dissolved by ammoniacal copper hydrate or concentrated sulphuric acid. 

 The inner portion of each consists of cellulose, but that of the oospore differs 

 from that of the oogonium in turning blue with iodine reagents instead of 

 purplish-violet, and in being insoluble in ammoniacal copper hydrate. 



The thicker, more hyaline apical portion of the conidium wall is not stained 

 by iodine reagents, and is insoluble in concentrated sulphuric acid and in 



