2 8o TIMBER AND SOME OF ITS DISEASES. [CHAP. 



the conidium bursts, and lets these minute motile 

 zoospores, as they are called, escape (Fig. 44, a). 



Each zoospore then swims about for from half an 

 hour to several hours in the film of water on the sur- 

 face of the epidermis, and at length comes to rest 

 somewhere. Let us suppose this to be on a cotyledon, 

 or on the stem or root. In a short time, perhaps 

 half an hour, the little zoospore begins to grow out 

 at one point or even at more than one and the 

 protuberance which grows out singly bores its way 

 directly through the cell-wall of the seedling, and 

 forms a cylindrical hypha inside (Fig. 44, b, c y e, 

 this hypha then branches, and soon proceeds t< 

 destroy the cells and tissues of this seedling. The 

 whole process of germination, and the entrance of 

 the fungus into the tissues, up to the time when it 

 in its turn puts out spore-bearing hyphae again, only 

 occupies about four days during the moist warm 

 weather in May, June, and early in July. 



We are now in a position to make a few remarks 

 which will enable practical people to draw helpful 

 conclusions from what has been stated. Let us 

 suppose a seed-bed several feet long and about three 

 feet wide, and containing some thousands of young 

 beech seedlings : then suppose that by any means 

 whatever a single conidium of Phytophthora omnivora 



