MISCELLANEOUS PAPERS. 25S 



about its habits, mode of growth, etc., in order to find the weakest 

 points in its life-history, or in other words, try to discover some periods 

 in its developments when we may expect to prevent its spreading, or 

 even destroy it. By a carefal study of the life-history of the apple 

 scab I think that I have found a number of these weak points, to which 

 it is my aim in this paper to draw your attention. 



The scab in question is a small plant, which has, like any other, a 

 reproductive and a vegetative system. It is called a parasite, because 

 it grows upon and derives its nourishment from another plant, although 

 at times it seems to take tbe shape of a saprophite. 1 mean when it 

 is growing upon dead leaves, as is often found to be the case, and thus 

 deriving its nourishment from dead organic matter. 



The plant-body of the parasite does not seem to penetrate deep 

 into the tissues of the host, but is usually confined to the epidermal 

 cells. It grows upon the fruit-leaves and young shoots. Upon young 

 shoots and dead leaves it is supposed to be perennial. It is reproduced 

 principally by spores, similar to the seeds of higher plants. These 

 spores are from 10 to 20u* in diameter, one-celled, though often they 

 are constricted in the middle, so as to have two cells. 



These spores live over winter in infected fruit and dead leaves. 

 They require a certain amount of heat and moisture to germinate^ 

 which is also the case with seeds of higher plants. Cold and moist 

 weather in spring seems to be most favorable for the germination of 

 these spores, as 40° to 50° F. is about all the heat they require. They 

 germinate in from eight to ten hours. This seems to be the way that 

 the fungus usually reproduces itself, though every cell of the plant- 

 body is capable of pushing out a germ-tube, similar to root-cuttings of 

 higher plants. However, as stated before, the scab is most generally 

 reproduced by means of the spores, which live over winter in infected 

 apples and dead leaves. These spores are carried about by the wind. 

 Whenever they get upon young leaves and apples, and the proper heat 

 and moisture is present, they will germinate in from eight to ten hours. 

 As soon as they germinate they push out a germ-tube, which penetrates 

 the cuticle, where a plant-body is formed among the epidermal cells. 

 I give all these matters in detail because I expect later to point out 

 some of the weak points in the cycle of the life of the fungus. 



It has been proven beyond a doubt that these spores germinate 

 more readily upon the surface of some apples than they will upon 

 others. The plant-body of the fungus, as stated before, is mostly con- 

 fined to the epidermic cells ; however, it soon breaks the cuticle by 

 sending out a lot of little threads about 50u in length, which will bear 



* 1 u ^ ^^0 P^^^ of ^^ inch. 



