PLATE i « 
A. —Mycelium of Sclerospora graminicola within a portion of a cross section of a 
badly infected Setaria viridis leaf cut at io p. m. The invading hyphae have pushed 
the mesophyll cells apart, and knobby branches have made their way into the air 
chamber under the stoma through which they will grow out and give rise to conidio- 
phores. At a, a small, bulbous haustorium has penetrated an epidermal cell, and 
at 6 a branch of the mycelium appears in cross section as it runs between the meso¬ 
phyll cells at right angles to the section. X 425. 
B. —A bit of Setaria leaf like that shown in A, but more highly magnified, and 
cut in longitudinal section somewhat later at night. The mycelium has invaded the 
tissue more extensively, and has developed in the air chamber a crowded group of 
proliferating branches, some of which are just about to push out through the stomatal 
slit. X 850. 
C. —Exterior view of a stoma in a piece of epidermis cut from an infected leaf of 
Setaria viridis at midnight. A knoblike protrusion has grown out from the proliferat¬ 
ing branches, which are shown crowded in the substomatal air chamber in 
B, and is pushing through the partly closed stomatal slit ready to elongate into a 
conidiophore initial. 12 p. m. X 375 * 
D-E.—Early stages in the development of the conidiophores of Sclerospora gramini- 
cola from the leaves of Setaria viridis , showing the elongation of the knoblike out¬ 
growths, seen in C, into club-shaped conidiophore initials. 12 p. m. X 375 * 
F.—Exterior view of a bit of the epidermis of a Setaria leaf, looking obliquely at a 
clump of young conidiophore initials arising from the almost obscured stoma, and show¬ 
ing various stages of development, from young knoblike outgrowths that have just 
emerged to older elongate stalks. At a is shown the base of a conidiophore already 
matured, and now shriveled and broken off; and, at b, a stoma as yet uninvaded by 
the fungus. 12 p. m. X 375 - , , 
G-O.—Later stages in the development of the conidiophores, showing the formation 
of the successive series of branches (primary, secondary, etc.), until finally at O the 
branch system is complete. 2 to 3 a. m. X 375. 
P.—A bit of the upper epidermis cut from an infected Setaria leaf at 3 a. m., and 
showing, in oblique view, a maturing conidiophore. This conidiophore is an unusually 
stunted one, bearing only eight still spherical and not yet mature conidia, on a reduced 
branch system of two primary branches each of which gives rise directly to four sterig- 
mata and conidia. 3 a. m. X 375. 
0 The drawings were made with the aid of a camera lucida, and are all of Sclerospora graminicola on Setaria 
viridis. A, B, C, F, and P are drawn from free-hand sections of living material cut at night in 
water, and immediately killed and fixed in Flemming’s weaker solution, stained, and mounted. D, 
E, and G to O are from material carefully scraped from productive leaves at night, and either drawn at once 
while still living, or drawn after being killed and mounted as were the sections. The approximate magni¬ 
fication of the printed figure after its reduction from the original drawing is given in each case, as is also* 
scale with iou divisions as an absolute measure. 
