A. S. HoiiNK 191 



Reed^ (1912) the Phytophthora of tomato is identical with that of the 

 potato. The formation of conidia upon hosts other than the potato 

 may therefore prove to be a source of infection and the cause of an 

 epidemic. 



A very attractive solution appeared to be in the possible discovery 

 of and wide occurrence of sexually-formed resting spores such as occur 

 in the related fungus Pythium. Oospores of Phytophthora are now 

 known, and chiefly owing to the work of Clinton^ who obtained them, 

 in pure cultures of the fungus in artificial media. In spite of diligent 

 and persistent search by numerous investigators, oospores, however, 

 have not yet been discovered within or upon the potato plant so that 

 they do not appear to be formed upon this particular host. There seems 

 to be no reason, of course, why oospores should not be found upon 

 some other host and be discharged to the soil from the host, but no 

 extensive study in this connection has yet been made. 



Another point that needs to be determined is whether the mycelium 

 of Phytophthora can maintain existence in the soil from the autumn 

 .until the following potato-growing season, either parasitically in the 

 many small potatoes remaining in the soil or saprophytically in frag- 

 ments of tuber and pieces of skin. 



Another phase of the Phytophthora problem must now be con- 

 sidered — the actual occurrence and mode of occurrence of the disease. 



Infection of the foliage may be brought about in two ways. Firstly, 

 the mycelium present in a planted diseased tuber might extend into 

 the growing sprout and thence into the leaves and infect them. Secondly, 

 the leaves might be directly infected by means of conidia, wind borne 

 or brought by some other means. In this case the zoospores liberated 

 from the conidia germinate forming mycelium which enters the tissue 

 of the leaf and causes it to droop and die. Spraying when properly 

 performed has been found an efficient remedy against the premature 

 death of the foliage ; the disease is checked and the growth of the 

 plant is actually stimulated. 



Tuber infection also may be brought about in two ways. Firstly, 

 in the case of plants with infected foliage the mycelium could extend 

 into and along the vascular bundles ultimately reaching the growing 

 tubers, but this method does not appear to be of frequent occurrence. 

 Secondly, the growing tubers might be attacked directly from the soil. 

 Irrefutable evidence of the frequent occurrence of this mode of infection 



1 Howard S. Reef! in Phijt. ii. (1912), p. 250. 



- G. P. Clinton in Science, N.S. xxxiv (1911), p. 744. 



