Peach Leaf-Curl. 375 



show the appearance of twigs in which the fungus is winter- 

 ing ; a, a twig of the same age which is perfectly normal ; and d, 

 a twig killed by the presence of the fungus in its tip. 



c. Life History of the Fungus. 



In this latitude it is usually the latter part of May that the 

 curl is most pronounced, and the grayish appearance is evident 

 soon afterward on all diseased leaves, and on both surfaces of 

 such leaves. The surface is evidently covered with a dense close 

 growth, somewhat mould-like in character. As previously 

 mentioned, the fungus which causes the curl is then fruiting, 

 forming the spores which are to disseminate the disease ; but this 

 cannot be seen by the ej^e alone. Examining under the micro- 

 scope some of the close growth scraped from the surface of dis- 

 eased areas, numerous short, erect, thread-like growths (fertile 

 hyphae)willbe evident, as in figure 67. Close examination at the 

 time that the fungus is mature shows that these erect hyphaeare 

 sac-like in appearance (the asci), and the}^ usually contain eight 

 oval bodies called the spores. In the asci the spores may sprout or 

 bud, forming numerous conidia. x\fter these spores or conidia 

 are mature, they are soon set free from the sac-like structures ; 

 and being so minute and light, they are ready to be borne about 

 by the wind. When they fall upon vulnerable parts of other 

 trees, they are in readiness to grow into the tissue and to pro- 

 duce the disease again. 



The fruit of the fungus is produced on the surface of the leaf, 

 but the true vegetative state of the fungus is within the tissues 

 of the leaf and of the young shoots. The threads, or filaments, 

 which make up this vegetative state pass in between the cells of 

 the leaf, and it is the irritation due to the presence of these fun- 

 gous filaments (the mycelium) which causes the leaf to become 

 distorted in form. Passing into the young shoot, the fungus is 

 in a condition to pass the winter in situ, provided the twig lives, 

 without having to trust to the fortune of winds and rains, as is 

 the case with the spore. 



It is unfortunate that the exact fate of the more fortunate 

 spores is not known. Since the second growth of leaves is not 

 badly infested by the curl, the spores do not produce the disease 



