135 



the tuber and other parts of the diseased plant ; also 

 that these could retain vitality independently of the 

 potato when once they had matured, all that was 

 necessary to bring them into activity being suitable 

 temperature and sufficient moisture. These spores, 

 on germinating, broke up into several spores, which 

 were easily transported by the wind, and if they fell 

 upon a potato plant when conditions were favourable 

 to their germination they immediately attacked it and 

 set up disease, the further development being regu- 

 lated by climatic influences. 



M. de Bary, however, demonstrates that there are 

 no resting spores to carry on the disease, but that the 

 mycelium within the tuber becomes dormant during 

 winter, but returns to activity in spring, when con- 

 ditions are suitable. This view is very largely ac- 

 cepted. It is, however, unfortunate that Mr. Smith's 

 view cannot be refuted on other grounds than that 

 others who have made investigations have been unable 

 to detect what he asserts he has seen. It may be abso- 

 lutely true that the resting spores do not exist, under 

 which circumstances they could not be seen ; but those 

 opposed to his view can only go so far as to say they 

 cannot detect them. On the other hand, some of the 

 Phytophthorce, the most closely allied sub- division of 

 fungi to the Phytophthora infestans, differing, even in 

 their microscopic size, only in the most minute degree, 

 are known to produce intersexual resting spores, which 

 carry on the disease from year to year. With this 

 knowledge it appears reasonable that their close re- 



