CONCLUSIONS REGARDING SPRING INFECTIONS. 43 



(lie |)i(>s(Mit remarks on infested uiul iioninfostod hraiu-lics.) It sccins 

 pi()l)ul)li', therefore, (1 ) that niostof the sprino- infeetionsof the peach 

 oeeiir from spores whieh have wintered on the tree and a))out tlie newly 

 formed Imds; (2) that most of the infected leav(\s fall off witiioiit 

 infecting the branch which bears them; (3) that the mycelium of badly 

 diseased leaves sometimes infects the branch through the h'af petiole; 

 (4) that such mycelium after entering the ])ranch may pass upward 

 or downward, and in some instances may follow the branch for the 

 length of one or at most a few internodes, and possibly infect one 

 or two adjoining buds; (5) that badly infested l)ranches usually die 

 durino- the vear, while in comparativ(>lv few instances they may suj)- 

 port a living mycelium capable of inducing spring infection of opening 

 budij; (0) that most infected branches show by external hypertrophy 

 the presence of the parasite, which may citnmioidy be removed by 

 pruning oti' the hypertrophied parts at a point a few inches l)elow 

 the swelling; (7) that seasons, atmospheric conditions, localities, and 

 varieties may have a limited bearing on the extension of the mycelium 

 in the branch and upon the amount of mycelium wintering in an 

 active state, although the results of spraying in many parts of the 

 country, contimied for several years, have shown the variation in 

 these respects to be confined within comparatively narrow limits. 



The direct infection of the peach leaf by means of the spores of 

 Exoascm def<yrmans has not been seen. The eliorts made to observe 

 the germination and penetration of the fungus have already l)een 

 touched upon. One thing seems certain, viz, that under ordinary 

 conditions this form of infection occurs at a very early period in the 

 development of the leaf, but evidently not before the opening of the 

 leaf buds. Veiy voung leaves are found to be already infected, but 

 spraying just before the buds expand will prevent this infection, i. e., 

 infection may be prevented by the treatment of closed Inids, which 

 would scarcely be true if a perennial mycelium were within. If we 

 may judge by analogy, the germ tube of the fungus enters the leaf 

 through a stoma. Sadebeck reports that such was his observation in 

 Exoascus tosquinetii^ in which species the germ tube creeps for a short 

 distance on the leaf surface, and then enters a stoma, much as in the 

 germination of the conidium of Phytophthora oinnivora. 



The major portion of the spring infection of foliage occurs while 

 the latter is young and tender, but it is observed that new infections 

 may take place for a considerable time if the various influencing con- 

 ditions continue favorable to the fungus. These conditions act chiefly 

 in suddeidy retarding the transpiration of the host, and some of them 

 have already been discussed. On the other hand, a short period of 

 spore infection may be expected when external influences are such 

 that transpiration is rapid and normal. The longer or shorter course 

 of the disease in spring may be said to depend largely, therefore, upon 

 the greater or less susceptibility of the tissues of the host, mostly 



