m 
LIFE-HISTORY OF HEMILEIA VASTATRIX. 3l; 
month (October 16th to November 15th) was occupied in bring- 
ing this leaf into full activity, and probably a fortnight must be 
added to the last column, during which time the mycelium was 
forming. How little of the total life and powers of such a leaf. 
benefited the tree will be evident on comparing these results. 
The method adopted in arriving at these conclusions was to 
mark a given vigorous twig, and note the progress of the bud, 
fungus, &c., at intervals of a few days. No other conclusions 
than those for which the tables are designed are intended to be 
drawn: e. g-in the example given, the date December 5th (in the 
6th column) does not mean that the first spore formed on that day, 
but that, taking notes of the progress of events on December 5th, 
I found spores were already formed by the spots in some quantity, 
whereas they were not present when notes were taken some days 
earlier, 
To take another example (K), we find a very different series 
of events when no mycelium or only an odd spot appears: here 
the bud of January 30th began to unfold in February, and reached 
its full development as a pair of leaves about March 10th. Up 
to June 26th no signs of disease had appeared ; and we notice that 
the traces of spots noted on July 6th never came to anything, 
as signified by “O” in the column. The leaf fell on August 10th, 
after a total life of 21 weeks or so. In such a case we may 
safely assume that its work was chiefly devoted'to the benefit of 
the tree. 
I shall have occasion shortly to point out the importance of 
the fact that one or two “ disease-spots”’ do not suffice to destroy 
the leaves: a luxuriant tree may support a certain amount of 
fungus, as well as a large quantity of fruit. Meanwhile attention 
may be directed to some experiments showing that the greater 
the quantity of mycelium (and therefore of “ disease-spots ") the 
Sooner the leaf falls (Table VI.). 
To take an example (F) : on December 20th the leaf was adult 
and in full working order. It retained its green, bright colour 
until April 2nd, when a few faint yellowish cloudy patches were 
observable, the signs of approaching dissolution. 
On April 25th the leaf had become yellow, like an autumnal 
leaf in Europe, and fell soon after, about May 3rd, having done 
its work for the tree, but having escaped the ravages of the myce- 
lium of Hemileia. 
LINN. JOURN.—BOTANY, VOL. XIX. 2» 
