44 PEACH LEAF CURL: ITS NATURE AND TREATMENT. 



resiiltin<j;- from atmospheric influences. The injuiy which the fungus 

 may do after infection is also dependent, where development of the 

 fungus has not progressed too far, upon a v^ery nice balance of the 

 atmospheric conditions. Newly infected leaves ma}' be greatly 

 distorted and fall at an early date, or they may be only slightly 

 injured by the fungus, according to the atmospheric conditions prevail- 

 ing and their influence toward softening or hardening the tissues and 

 moistening the intercellular spaces of the host. A few days favorable 

 to the drying and toughening of the parenchyma of the infested Leaf 

 may entirely check the spread of the fungus. The action of the 

 mycelium of E. deformanH upon the tissues of the leaf and branch of 

 the peach has been widely remarked. The hypertrophies of peach 

 branches, due to this parasite, are as striking and characteristic as are 

 the witches' brooms caused on other hosts by various Exoascece. In 

 the case of the peach, however, there is rarely if ever any increase 

 noted in the number of shoots, as upon the cherry, the hypertrophy 

 manifesting itself in enlargements and twistings of the infested 

 branch. There is often a great reduction in the length of the infested 

 portion of the shoot and a shortening of the internodes, so that the 

 approximated and enlarged leaves give a tufted or plumed appearance 

 to the shoot. An examination of transverse sections of such enlarged 

 shoots shows that the enlargement is due to a great increase in the 

 number of cells of the cortical parenchyma, and frequenth^' an entire 

 separation of such cells into a network or series of chainlike cells. 

 The structure of the infested parenchyma is altered, the cells being 

 enlarged and much more angular than normally, while the thickness 

 of the tissue from the bast fibers to the epidermis is frequentl}^ eight 

 or ten times as great as usual. The parenchyma cells lose the chloro- 

 phyll and all matter which the eye can detect, becoming quite trans- 

 parent. The cell walls vary much more in thickness than normally, 

 some of them being heavier and others lighter than in healthy cells. 

 Transverse and longitudinal sections of swollen peach twigs show that 

 the pith cells are greatly injured along the course of the infesting 

 mycelium. The location of the mycelium may often be detected by 

 treating transverse sections with Bismark brown, the infested medul- 

 lary tissue taking less stain than that not harboring the fungus. The 

 walls of the healthy cells of the medulla become reddish brown, while 

 those of the infested tissue assume scarcely more than a light 3"ellow 

 or yellowish brown. The cells of the infested tissue are also much 

 more angular and irregular than those in which the mycelium does 

 not exist, while in some instances the cells collapse. 



The action of E. deformans on the tissues of the peach leaf has been 

 considered by difierent writers, as Prillieux.^ Knowles,^ and others. 



'Prillieux, Ed., Mai. d. Plantes Agr., Vol. II, pp. 394-400; also Bull, de la Soc. 

 Bot. de France, 1872, T. XIX, Comp. Rend. d'Sci., 3, pp. 227-230. ' 

 ^Knowles, Etta L., Bot. Gaz., 1887, Vol. XII, pp. 216-218, with plavo 



