PLATE 2 a 
A.—A conidiophore of Sclerospora graminicola with the branch system completed 
and its ultimate tips elongating into sterigmata which will give rise to the conidia. 
The wall at the base of the main axis is thickened into a differentiated, footlike portion. 
X 375 - 
B-F.—Successive stages in the development of the conidia from the tips of the 
sterigmata. Note that at a relatively early stage, the wall at the tip begins to thicken 
and becomes modified into the characteristic apical papilla of dehiscence. X 850. 
G. —Mature, recently shed, conidium with well-developed papilla of dehiscence at 
its apex, and the small apiculus by which it was attached to the sterigma still per¬ 
sistent at the base. The content has not yet begun to divide into zoospores, but is 
still undifferentiated and granular. X 850. 
H. —The empty wall of a conidium (i. e., zoosporangium) which has germinated by 
emitting zoospores through the pore left by the softening and dissolution of the terminal 
papilla of dehiscence. X 1,200. 
I. —Conidiophore at a later stage than that shown in A, with a vigorous, well- 
developed branch system which bears 18 only partly developed conidia. These 
conidia are still spherical, and have not as yet developed the terminal papillae of 
dehiscence. X 375. 
J. —Detail of a branch tip of the three-pronged type frequently encountered (cf. 
ffg. 1). Note that the young conidia which are just beginning to develop from the three 
sterigmata are not of exactly the same stage of development. X 600. 
K. —A large, well-developed conidiophore which has shed all but two of its conidia. 
The branch system shows a somewhat extreme case of the continuing of the main 
axis, a characteristic of Sclerospora graminicola . An attempt has been made to show 
the detail of the content as it appears when the conidiophore is at this stage. An 
incomplete septation at the base delimits the basal cell which is occasionally en¬ 
countered in this species. X 375 * . ... , 
L. —A still more extreme case of continuation of the main axis in the branch system 
of the conidiophore. X 375 * 
M. —Representative conidia showing the various shapes and sizes most frequently 
encountered. Note that each has a terminal papilla of dehiscence. The content, 
which is conventionally stippled here, is shown in detail in G. X 375 * 
N. —Detail view of two conidia still in place but already mature and about to be 
shed from the sterigmata. X 600. 
O. —Typical, vigorous, well-developed conidiophore, like that in figure 1, but 
in a later stage of development. This is shown by the maturity of its 24 conidia, 
their larger size, more rotund ellipsoidal shape, and prominent papillae of dehiscence. 
Note the absence of any foot cell or basal thickening of the main axis wall. 2 a. m. 
X 375 * 
P. — A small, stunted conidiophore. The branch system, in comparison to that of 
a typical well-developed individual such as the one shown in O, is much reduced. 
Its three primary branches give rise directly to eight sterigmata and conidia, 
which, however, are larger than the more numerous ones of O. Note that the wall 
of the main axis is thickened at its base. 3 a. m. X 375. 
Q. —A typical, well-developed conidiophore which only recently has shed its 34 
conidia, as is shown by the bottle-shaped and rounded tips of its sterigmata, and by 
the beginning of the disintegration of its content. 3 a. m. X 375. 
R. —The shriveled and shrunken remains of such a conidiophore, which had de¬ 
veloped during some previous night, and had remained, dried, on the leaf until scraped 
off and examined during the day. X 375 - . 
S. —A similar, mummied conidiophore, but one more completely shrunken and 
collapsed after longer drying. X 375. 
T. —Detail of a branch tip of the dichotomous type so frequently encountered. 
One sterigma still bears a mature conidium; while the other by its bulging, rounded 
apex shows that it has only recently discharged. 
U. —Detail of a similar branch tip with one typical, short sterigma which has already 
shed its conidium, and one rather unusually elongate sterigma bearing a conidium 
only partly developed. X 600. 
V. —Detail of a branch tip with six sterigmata which have a somewhat uncommon 
arrangement resembling slightly that of the sterigmata of Bremia. X 600. 
W. —A branch tip of a type frequently encountered, showing four approximately 
equal pronglike sterigmata standing out at equal distances from the club-shaped 
branch tip. X 600. 
X-Y.—Typical examples of the kind of basal cells occasionally found in coni- 
diophores of Sclerospora graminicola. X 375. 
Z.—Base of a conidiophore showing the thickened w T all that at times marks off a 
differentiated foot portion instead of a basal cell. X 375- 
a The drawings were made with the aid of a camera lucida, and are all of Sclerospora graminicola on 
Setaria viridis. Figures H and I were drawn from living material; the others from material scraped from 
leaves bearing abundant conidiophores at the time of maximum nocturnal production, and immediately 
killed with Flemming's weaker solution, stained (chiefly with eosin), and mounted in dilute glycerin. 
The approximate magnification of the printed figure after its reduction from the original drawing is given 
in each case, and also a ion scale is shown as an absolute measure. 
