262 Wisconsin State Horticultural Society. 



which ihey alight, the spores whether simple, conditional or zoo- 

 spores, germinate at once, sending out a mycelium which enters 

 the nearest breathing pore and penetrates the cellular structure of 

 the leaf in every direction. Once established their growth is very 

 rapid; spore-bearing stems startup through the stomata under 

 which the mycelium extends, and in a very few hours the second 

 crop of spores is matured. Zoospores have been known to ger- 

 minate, pass through all the stages of growth and to produce a 

 crop of ripe zoospores in twenty-four hours from the time they 

 were given the necessary conditions. Where these conditions are 

 wanting, either in whole or in part, growth is prevented or much 

 retarded. Spores falling on a healthy leaf while covered with 

 moisture, may germinate and send its mycelium into the stomata, 

 filling the air cavity underneath it, but not finding suitable nour- 

 ishment in the leaf " while it is kept in a living, vigorous condi- 

 tion by remaining attached to the plant, no further change will 

 appear ; the germs may remain in the same condition, dormant, 

 yet fresh, for days and even weeks." Again, on the other hand, 

 the fungus has been seen to make slow growth and gradually to 

 extend through the plant when the climatic conditions, regarded 

 as essential to its very existence, were entirely wanting, and such 

 instances have been cited to prove that the fungus was not de- 

 pendent upon conditions, but an active primary cause. Is it not 

 more natural to infer that in the first instance that as long as the 

 vitality of the leaf was maintained it had no power to injure, and 

 in the second that it found favoring conditions in the plant which 

 alone made its development possible. 



To the methods of reproduction already mentioned, there is 

 but little doubt that there must still be added, to get a full his- 

 tory of the development of the fungus, the formation of winter 

 or resting spores, as they are called by Professor Smith. The 

 manner of their development, as observed by him and others, ap- 

 pears to be identical with that seen in the related species of fun- 

 gus growth already mentioned. In the mycelia which traverse 

 the tissues of the plant, there is seen to be quite a difference in 

 form and size. Some of the threads are much larger than the 

 others, and on the larger threads, at certain periods of their 



