Jan. 27,1923 
Production of Conidia in Philippine Sclerosporas 261 
The third factor, environmental conditions favorable for conidium 
formation, bears on the quantity of conidia produced as follows: Under 
the usual field conditions, when the infected plants have begun to show 
the characteristically discolored areas, and these have begun to bear 
conidia, the number borne is at first comparatively small, as the coni- 
diophores are few and scattered. As time goes on, however, and conidio- 
phore production is induced night after night successively, production 
rapidly increases until on the area already established it attains its maxi¬ 
mum density. This maximum density under such favorable environ¬ 
mental circumstances may occur even before this area has reached its 
maximum size. On the contrary, if such a plant has been exposed to 
conditions preventing conidiophore production, the area, even though 
long established, will not produce large numbers of conidiophores until 
favorable conditions have prevailed for so long a time that conidium 
production has been enabled to build itself up to the maximum. 
It is apparent, therefore, that a plant to produce a maximum quantity 
of conidiophores must have: First, a large conidiophore-bearing surface; 
second, a large number of stomata per unit of this surface; and third,, 
continued favorable conditions which permit conidiophore production 
to increase night after night to its maximum. These requirements are 
fulfilled in such typically Philippine varieties as Moro White, Native 
Yellow, and Cebu White, or in the even larger introduced dent and flint 
types. After studying conidiophore production on such varieties at 
night, and finding plant after plant with the greater part of its leaf 
surface white with a felt of densely grouped conidiophores (PI. 4, C, D), 
and after seeing the thousands of spores which fill even a minute droplet 
scraped from the surface of such a leaf, one is impressed by the vast 
production of conidia which goes on. To get a more definite conception 
of this vast production the writer made approximate estimates of the 
number of conidia formed on typical plants. These estimates were calcu¬ 
lated as follows: The total surface bearing conidiophores was multiplied 
by the number of bearing stomata in a unit of surface, and this result by 
the average number of conidiophores from each stoma, and this in turn 
by the average number of conidia per conidiophore. For the conidiophore- 
bearing surfaces the measurements recorded in Table II were used. For 
the number of stomata the averages of Kiesselbach were employed, but as 
microscopic examination showed that usually only about one-half the 
stomata actually bore conidiophores the averages, 77 above and 93 below 
per square millimeter of surface, were reduced accordingly. The number 
of conidiophores bearing conidia at each stoma when examined at different 
times during the night was found to vary from one to four, with two as a 
conservative average. From the number of club-shaped initials in various 
stages of growth at each stoma the number of conidiophores successively 
developed per stoma during the nightly cycle was approximately esti¬ 
mated as six or three successive “ crops” of two each. The number of 
conidia on the conidiophores, although very variable, most commonly 
ranges from 32 to 48; 40, therefore, was selected as a fair average. The 
results of the calculations are shown in Table III. 
These figures may serve to give a clearer idea of the amount of conidium 
production on a diseased plant than can be obtained merely from descrip¬ 
tion. They are, of course, only approximate; but they are extremely 
conservative, and purposely have been made to underestimate rather than 
overestimate the number. Obviously a single diseased plant, even a 
