LIFE-HISTORY OF HEMILEIA VASTATRIX. 311 
no reason to suppose these plants other than fair subjects for expe- 
riment. 
A sowing of spores was made on the underside of a chosen 
leaf on nine different days from October 5 to 25, in the manner 
already described, with fresh, ripe, moist spores; and a slowly- 
dropping siphon played on the damp chamber for four days. On 
the fifth day the damp chamber was removed in each case, and, 
with a perfectly clean sponge filled with pure water, the adhering 
spores &c. were then washed off—the detection of the young 
" disease-spot" at its earliest appearance being thus rendered 
easier. Theleaves were closely examined daily, and the following 
Table (TII.) gives the summary of observations. 
B. Nine young seedlings of C. arabica were selected which 
had been raised in pots in a closed Wardian case, and in soil 
. dug from a depth with great care. Each seedling possessed its 
cotyledons, and one pair of thin, apple-green, succulent, and 
healthy leaves of a fortnight's growth; the second pair of leaves 
were just appearing. The sowings &e. were made exactly as 
before; and all circumstances were the same, except that the 
Wardian case in which these experiments were conducted stood in 
another room. I have no reason, however, to believe that the very 
small differences in the amount of light, air, &c. which may have 
existed could materially influence the results. The temperature of 
both rooms was nearly the same, viz. 759-789 Fahr. on the average. 
The results are appended in Table IV. 
It appears impossible to avoid the conclusion that, generally 
speaking, the thinner and more tender the leaf, the more rapidly 
does the “ disease-spot ” appear. If it be objected that the older 
plants, having travelled from Samarang some months before, were 
not fairly compared with the Ceylon seedlings, it may be justly 
remarked that the young and tender leaves on these plants also 
developed the spots more rapidly. 
If, in the above instances, we take the average number of days 
occupied in producing the spots on the old leaves and compare 
with the time occupied in the case of the young ones, however, the 
difference is very striking: the numbers are *? — 15 days, against 
129 — 102 days, for the old and young leaves respectively. 
I do not imagine that the differences in the rate of develop- 
ment of the spots in the above cases were due simply to differ- 
ences in the rate of infection. It has already been stated that 
freshly ripened spores produced in the moist season germinate 
rapidly ; and it will be noted that slowly-dropping siphons were 
