PARASITIC ON PELLIA EPIPHYLLA. 115 
chance of success. A large number of my sections showed clearly 
that direct infection had occurred: single isolated cells of the 
superficial layer presented the characteristic brown collapsed 
appearance. I could repeatedly trace a hypha froma spore to a 
browned superficial cell, from which cell I could trace a hypha 
through the next cell towards the central tissues, but I could not 
demonstrate the continuity of these two pieces of hypha. I 
felt perfectly sure that the obtaining of an ideal preparation was 
only a matter of time; and I continued to cut, mount, and examine 
in water sections of the thallus that I had infected from the 
spore-clusters on the host and from tube cultures. At this 
Juncture Professor Marshall Ward advised me to mount my 
sections in a one-per-cent. solution of potash; and I cannot say 
too much in favour of such a practice, for I feel confident that 
much of my labour would have been spared by its use, and I 
should have thereby saved much time and valuable material. 
However, on Tuesday, July 14th, I obtained among many others 
the preparation shown in PI. 7. fig. 33, which is specially interesting 
as the thallus from which it was cut had been infected from a tube- 
culture. My preparations, therefore, demonstrated the parasitism 
of the fungus, for I had taken its spores from the host, had 
cultivated the fungus, and with the spores from a pure culture 
pe alle to infect the host-thallus and to produce on that 
trace " e appearances characteristic of the disease, and had 
Such | " actual infection of the host through its upper surface. 
the oul ection can only be parasitism. All the cells were alive, 
of the d dre of approaching alteration being the brown tinge 
and "i and this due to the enzyme produced by the spore 
matter ARE there was no nursing of the fungus on dead 
thallus vith Thad been very careful to place spores only on the 
The thal no admixture whatever of any nutrient material. 
removed »" remaining after material for sections had been 
would doy allowed to live on in the laboratory to see if it 
lsease and the same macroscopic optical characters of the 
as in the ori ane the disease would spread along the thallus 
have thestar es and it did so. etic 
fungus has tak een able to satisfy myself that a saprophy 
uncommon ex a on à parasitic phase. It is by no means i 
stance of the P Some three years ago I saw a vey go 
tarden, where me phenomenon at the Cambridge Botanic 
eheraini Spores of Botrytis, growing on a dead twig of 
ma, had fallen on to a leaf of Adriopsis immediately 
12 
