324 Bulletin 73. 



trophied organs of the various species of Prunus, and the mor- 

 phology and structure of the infecting species of Exoascecz. 



Prunus Persic a (L). Peach. 

 Exoascus deforma7is (Berk.) Fuckel. 



The leaves and twigs are the only portions of the peach tree 

 which are at present known to be affected with the fungus. The 

 leaves are more commonly the place for the injury to be shown, 

 and the twigs are but rarely attacked seriously or so as to attract 

 attention. During June, 1894, I observed a tree on the Cornell 

 University Campus having the leaf "curl " and a few of the ends 

 of certain twigs were abnormally enlarged, though but slightly. 

 One of these is reproduced from a photograph in Plate I, Fig. i. 

 The petioles of the leaf are also hypertrophied and profusely cor- 

 rugated. From the petioles the hypertrophy can be seen to 

 extend part way on the stem. Scribner* notes quite a serious 

 injury to young shoots of nursery trees received from New York 

 and transplanted at Knoxville, Tenn. The shoots for several 

 inches below the leaf bud were considerablj?^ enlarged and pre- 

 sented a very much roughened or corrugated surface. 



The disease in the leaves produces the distortions which are 

 commonl}^ spoken of as "leaf curl." With the increase in the 

 number and size of the cells of the affected part the leaf is thrown 

 into a series of irregular folds frequently transversely to the long 

 axis of the leaf. Sometimes the arching of the leaf takes place 

 more strongly on one side than on the other when a strong con- 

 vexity appears on that side. When a large portion of the leai 

 is thus affected it frequently bulges out on one side along the 

 middle and the edges of the leaf are drawn toward each other, 

 the leaf appearing as if strongly inflated. In the affected por- 

 tions of the leaf the green color pales and the parts are more or 

 less brightly colored with reddish or yellowish tints. The leat 

 tissue at these parts is also thickened and assumes a ' ' cartilagin- 

 ous" consistence. The parenchj^ma cells are frequently very 

 much elongated and curved or sinuous in form. The mycelium 

 is perennial in the leaf buds, that is, it passes the late summer, 

 autumn and winter mouths in the tissue of the leaf buds and in 



Fungus diseases of the grape and other plants, p. 126. 1890. 



