io6 Journal of Agricultural Research voi. xix.no. 3 



parts of the plant but to a lesser degree affects the male and female 

 inflorescences also. 



Since the mycelium is relatively inconspicuous, its course throughout 

 the host tissue is followed with difficulty. However, by means of trans- 

 verse and longitudinal sections cut in various thicknesses and stained 

 with iron-alum-haematoxylin and eosin or with gentian violet or methyl 

 blue it was possible to trace the relation of the hyphae to the host tissue. 

 Moreover, by subjecting such sections to the processes of maceration, 

 clearing, and subsequent staining used by Mangin (13) and Berlese {2) 

 the host tissue was readily dissociated and cleared sufficiently to permit 

 the examination of large sections of the mycelium. By these methods 

 material was studied from all parts of plants in various stages of infec- 

 tion, and the nature of the hyphae, their relation to the host tissue, and 

 their location and abundance in different parts of the host were ascer- 

 tained. 



The hyphae are most abundant in the discolored areas of the infected 

 leaves but may be found throughout the plant in unmarked parts of the 

 leaves, in the branch tips of the apparently unaffected tassel, and at the 

 base of the seemingly healthy stem some feet below the first discolored 

 leaf. 



In the leaf sheaths, leaves, and such modified foliar structures as the 

 husks and glumes, the mycelium is most abundant among the cells of 

 the bundle sheaths and in the mesophyll tissue (PI. 23, E), but occa- 

 sional hyphae are found in the fundamental tissue and even among the 

 elements of the bundles themselves. 



In the stem, ear shanks, cob, and tassel rachis, the mycelium follows 

 the bundles, running for the most part parallel to them among the cells 

 of the bundle sheath (PI. 23, B) and less frequently sending out hyphae 

 more extensively into the surrounding fundamental tissue. 



In badly infected ears the mycelium usually runs out from the cob 

 along the funicvlus of attachment into the undeveloped parts of the 

 abortive kernels, and occasional hyphae are encountered even in the chaff, 

 seed coats, and endosperm of the apparently healthy kernels, though 

 not in the embryo itself. 



Wherever found, the hyphae are almost invariably intercellular in 

 position, occupying even the smallest spaces between the cells, and even 

 forcing adjacent cells apart as they grow between them. Occasionally 

 hyphae were seen which apparently passed within the cells, but the 

 interference of the host tissue was such that their position could not be 

 ascertained with entire certainty. Since the size and shape of the hyphae 

 are determined to a large extent by the nature of the intercellular spaces 

 which they occupy, there is very little regularity in these characteristics 

 in most cases. When separated by maceration, the hyphae are seen to be 

 of two general types — namely, the long, slender, occasionally branching 

 hyphae which lie alongside the vascular bundles in the stem and leaves' 



