318 Transactions. 



• 

 the seed of this weed that I have examined masses of resting 

 mycelium have been found in the tissue interior to the aleurone 

 layer. This mycelium remains inactive until the Lolium seed 

 begins to germinate, when it develops and keeps pace with the 

 growth of the host, and finally re-foims resting mycelium in the 

 developing seed. No mode of spore-formation, either sexual 

 or asexual, has ever been noted, and the fungus appears to live 

 in perfect harmony with its host. This almost symbiotic union 

 between the fungus and host is of the utmost biologic importance 

 in the economy of hybemating mycelium, for it is at once ap- 

 parent that if the fungus can live on its host throughout the 

 dormant season without causing any marked injury, there is all 

 the more chance of the host developing in a normal and more 

 or less healthy manner during the next season, and thus allow 

 the perpetuation of the fungus ; whereas if the resting mycelium 

 caused serious pathological changes in the host, the latter would 

 probably be killed outright, and the resting mycelium would 

 die at the same time. 



A considerable amount of material has been examined by 

 me during the past three years, showing both the ordinary and 

 the hybemating mycelium of Phytophlhora infestans, and a cer- 

 tain amount of interesting information on the perpetuation of 

 this fungus has thus been gathered together. 



The exact manner by which the mycelium of P. infestans 

 reaches the tuber has not been as yet satisfactorily ascertained, 

 and for this purpose detailed and careful examination in the 

 field would be necessary. Two methods have been suggested — 

 firstly, that the mycelium spreads from the leaf downwards 

 through the stem until it reaches the tuber ; and, secondly, 

 that spores developed on the conidiophores fall to the ground, 

 and are washed by rain or carried by other agencies directly 

 on to the surface of the tubers. I am inclined to think that 

 both these processes occur in nature, but that the mycelium, 

 which descends down the stem and then enters the tubers, 

 alone forms hybemating mycelium, and that the spores which 

 reach the tubers by mechanical and other means do not develop 

 into resting mycelium, bul are more or less directly responsible 

 for the rapid rotting that so often occurs with Phi/tophthora 

 attack. This view gains j>reat weight from the fact that healthy 

 tubers mi the surface of which Phytophthora spores are scattered, 

 but on which resting mycelium has not heeii observed by me, 

 rapidly develop a rot. Recently Matruchol and Molliard have 

 declared that Phytophthora docs do1 of itself cause a rot in potato- 

 tubers, but that after the tubers become affected the rot that 

 sets in is due to microbes that become associated with the P. in- 

 festans. This view, notwithstanding the high r authorities! from 



