36 PEACH LEAF CUEL: ITS NATURE AND TREATMENT. 



The fruiting hypha? have been seen to arise in Exoascus deformans 

 from the vegetative hyphse after the latter have become well developed 

 in the parenchvma of the leaf. Large, well-nourished vegetative 

 hyphse commonly develop just below the epidermal cells of the upper 

 leaf surface.^ From these hyphse arise branches which penetrate 

 between the cells of the epidermis, and press themselves between the 

 epidermis and the cuticle. Such hyphte may be seen both in section 

 and surface view. These subcuticular hyphte now branch freely, and 

 follow" with more or less regularity the triangular space formed b}^ the 

 juncture of two adjoining and somewhat rounded epidermal cells with 

 the cuticle. This is presumably the line of least resistance to the 

 advance of the hyphas. By opening and following these channels the 

 mycelium assumes the outlines of a quite uniform network beneath the 

 cuticle. While this manner of following the line of juncture of adjoin- 

 ing epidermal cells with the cuticle is common, it is not invariabh' the 

 practice of the fungus, cases occurring where apparently no such 

 agreement exists. Series of straight and parallel hyph^, at regular 

 distances apart, are sometimes met with beneath the cuticle as the 

 precursors of the hymenial layer. These send off lateral branches on 

 either side, which l)y enlarging, Ijranching, and curving eventuallj'^ 

 occupy most of the surface of the epidermis between the main hyphse. 

 It is probable that the path followed by the first subcuticular hj-phse 

 depends largely upon the firmness with which the cuticle is attached 

 to the epidermal cells, and which may largely depend upon the amount 

 of water in the tissues and upon the age and rapidity of their growth. 

 With the leaf tissues full of water and making a rapid growth, the 

 hypha? could naturally pursue a more direct course beneath the cuti- 

 cle than under contrary conditions. After the establishment of a 

 much-])ranched filamentous network of subcuticular hypha?, the cells 

 of which are usually slender, of medium length, thin-walled, and of 

 comparatively uniform diameter (PI. II, fig. 6), these cells begin to 

 distend, and are shortened by the formation of new transverse septa 

 (PI. II, fig. 7, and PI. Ill, fig. 22). About this time all septa become 

 much more distinct. At a later stage the cells become still more 

 distended and subspherical (PI. II, fig. 8). As these enlarged cells 



1 Miss E. L. Knowles (Bot. Gaz., Vol. XII, No. 9, p. 217) has called atten- 

 tion to the fact that Winter's statement that "the asci break through the lower 

 side of the leaf" does not hold good for the peach (Kryp. Flora, Asco., p. 6, and 

 Krank. Kultur-Gewachse, Leipzig, 1878, p. 47) . Winter is not alone in stating that 

 the asci of E. defonnans arise on the under surface of the leaves. Robinson says: "The 

 asci are borne on both sides of the leaf, but in greater numbers upon the lower sur- 

 face" (Robinson, B. L., Notes on the Genus Taphrina, Ann. Bot., Nov., 1887, Vol. I, 

 No. 11, p. 168) . Atkinson also says: "The asci are developed on both surfaces of the 

 leaf" (Atkinson, Geo. F., Leaf Curl and Plum Pockets, Cornell Agr. Exp. Sta. Bull. 

 No. 73, 1894, p. 325) . These and other like statements have probably arisen from a 

 study of other foliage than that of the peach, and of otlier species of Exoascus, and 

 qave been perpetuated through insufficient reference to nature. 



