310 MR. H. MARSHALL WARD ON THE 
Apart from accidents during the formation of the germinal 
tube*, therefore, it is clear that in a given experiment the act of 
infection by any one tube may be delayed or hastened according 
to the previous state of the spore as regards moisture &c. The 
outcome of my observations in this connexion is, that while the 
act of infection or entry of the germinal tube through the stoma 
may commence in 12 hours after the sowing of the uredospore, 
it may require 3 days or more. Nevertheless 40 to 48 hours is a 
very common period for the completion of this process. 
Having taken thisinto account, however, and made experiments 
under such circumstances that the germinal tubes are found to 
be completely formed and entering the stomata during the second 
day, I find that several other factors complicate the question as 
to the period occupied in forming the spots. Not only does the 
vigour of the mycelium depend upon the amount of food and 
moisture present in the leaf, but also on the ease with which the 
proper materials can be obtained and assimilated. It is there- 
fore clear that the age and condition of the coffee-leaf may influ- 
ence the rate of development of the parasitie mycelium within it: 
(N.B. This has nothing to do with the infection itself; the 
difference is important.) We have seen that the period at which 
the yellow “ disease-spot" makes its appearance depends upon 
the progress made by the mycelium in its work of destruction of 
the tissues: this may be affected by the thickness of the walls of 
the cells which are to be invaded, and also by their number in a 
given area of the leaf. The connexion between all these facts and 
the general healthiness and activity of the tree are obvious, whence 
must be inferred that any thing affecting the one may indirectly 
affect the other. 
I will now describe a further series of experiments showing the 
kind of evidence which exists in fact for the above views. In 
October 1881 I commenced two series of experiments as follows :— 
A. A number of plants of Coffea arabica were selected, which 
had been obtained from Samarang in a Wardian case, and had 
been two months in a cool, carefully ventilated room. These 
plants were one year old, still retained their early leaves, were 
healthy, dark green, producing new shoots and leaves. They 
had been removed without disturbing the rootlets, in each case 
a large cube of the original soil having been retained. There was 
* Such as non-contact with a stoma, the attacks of insects, fungi, &c. 
