jan. 27,1923 Production of Conidia in Philippine Sclerosporas 241 
infection through suckers, as well as the inconspicuously marbled mark¬ 
ings described later in this paper as the result of preventing the access of 
dew or other moisture to infected leaves, are of this kind. 
Certain markings, however, are always associated with conidiophore 
production. The most common of these have been described and illus¬ 
trated by the writer (24) for the maize downy mildew of the Philippines, 
by Butler (3) for that of India, and by Palm ( 16) and Rutgers (20) for that 
of Java. The photographs, diagrams, and colored plates in these papers 
show the general characteristics and the range of variation in color and 
pattern of these markings. Consequently, no further description is 
necessary at this point. 
It should be noted, however, that as a rule the markings associated 
with conidiophore production are progressively more extensive on suc¬ 
cessive leaves. This is especially noticeable in those markings which, 
because of their extremely pale color and large areas, are particularly 
conspicuous; and which, because they are associated with excessively 
abundant conidiophore production, are of especial concern to us here. In 
general, a leaf showing such marking has at the base a more or less ex¬ 
tensive solidly discolored area from which irregular, jagged, tongued 
protrusions extend toward the tip. On the lowest leaf attacked (which 
may be any from the second or third up to the eighth or ninth) this 
discolored area is confined to a small portion of the base of the blade, 
while on each successive leaf the area increases in extent and the irregular 
protrusions run farther and farther progressively toward the tip, until 
on the last leaves the yellowish white discoloration occupies the whole 
blade (fig. 1). 
The development of this pale color throughout these leaf markings of 
the diseased plant is a gradual one. When infected but as yet normal 
plants are kept under constant observation during the appearance of the 
disease symptoms, it is noticed that in the normal dark green of the 
leaves that are already unfolded, areas of the characteristic shapes that 
have been described, pale gradually through a yellowish green, then 
yellow, to a yellowish white color. The process is usually a gradual one, 
requiring several (6 to 24) hours from the beginning of the first difference 
in shade until the assumption of the final persistent whitish color. Since 
this loss of color is due to changes in the chlorophyl-bearing cells of the 
leaf brought about by the invading hyphae of the parasite, it is remarkable 
that so decided an alteration can be effected in what is relatively so short 
a time. The whitening of these areas may take place apparently at any 
hour, but in most cases observed it has been seen to occur during the 
night or in the early morning. 
It should be emphasized particularly that the extent of these discolored 
areas is established at the beginning, and no increase in size takes place 
as time goes on. If, as soon as the discolored areas of an infected plant 
have paled sufficiently to be distinguished, they are outlined lightly with 
waterproof ink, it can easily be seen that when once defined they never 
grow out toward the tip of the leaf, but their outlines remain unchanged 
in extent. Moreover, if in a downy-mildewed plant one dissects out the 
young leaves, on the tips of which the markings can be seen as they unroll 
from the bud, the discolored areas on the inclosed part of the leaf will be 
found already faintly defined. These faintly distinguishable areas may, 
to be sure, expand somewhat as the unrolling leaf expands to its normal 
dimensions, but they show no progressive growth once the marked areas 
are established. 
