LIFE-HISTORY OF HEMILEIA VASTATRIX. 315 
to have been formed in the moist atmosphere. The development 
of new spores may also be shown to proceed on leaves which have 
fallen to the ground, and in which a supply of food and moisture 
is still afforded to the spore-producing mycelium. 
The time during which the production of disease-patches and 
spores on a leaf may continue must necessarily depend upon a 
number of circumstances. Where one disease-spot only occurs 
on a coffee-plant, it may go on forming spores for many weeks. 
In given cases I have observed this process for from 10 to 16 
weeks and longer ; but if several spots form on the same leaf, their 
period of activity is shortened by the premature fall of the leaf. 
It may well be, also (though I have no direct proof of this) that 
in the latter case each spot produces fewer spores in a given time; 
since, where there is a struggle for food-supplies among several 
independent mycelia, it is unlikely that all are as abundantly 
supplied as one would be. 
The following Table (V.) summarizes the results of observa- 
tions made to determine (1) how long a time is oceupied by the 
coffee-plant in forming a complete pair of leaves, (2) at what period 
they become attacked by the fungus, and (3) how long they sur- 
vive the ravages of the pest. In all the specimens selected there 
were several of the disease-spots on each leaf; but, of course, ng 
absolute standard of the damage done is given. The following 
example will illustrate the mode of reading thecolumns. Taking 
the specimen F, the minute terminal bud evident so early as 
September 6th, 1880, remained quiescent during forty days (till 
October 16th), and then commenced to swell and unfold its pair 
of leaves. In about a month's time (November 15th) the leaves 
were completely formed and in full activity, and apparently clean 
and healthy. November 18th was the last date on which no trace 
of disease was visible to the naked eye; but it is evident, from 
what is known of the periods in the life-history of Hemileia, that 
the germinal tubes had already entered the stomata, and formed 
mycelia; for on November 23rd the yellow spots were apparent, 
and had developed spores before December 5th. The formation 
of spores continued, and the leaf was badly diseased with ^ rust- 
patches" before December 22nd, when the spots were already 
old and turned brown. On January 1st, 1881, the leaf had fallen; 
and an examination of the last two columns shows that, out of 
24 months' term of life, the leaf was obviously pestered with the 
fungus half thetime. Moreover, we must recollect that nearly a 
