16 SALMON: SUPPLEMENTARY 
greenhouse, the conidia differing from those of the Osdium on 
Celsia in being smaller and in possessing distinct fibrosin-bodies. 
It is clear, therefore, that infection must have taken place by some 
means from the adjacent cinerarias. 
In the second case, some rose bushes in a garden were observed 
covered with an Ozdium, and it was noticed after a few days that 
an Ozdium had now appeared on some adjacent raspberry suckers. 
To ascertain if the rose-Ozdium had really, as it appeared, spread 
from the rose to the raspberry, the following experiment was car- 
ried out. The raspberry suckers, mentioned above, which were 
attacked by the Ozdium, were situated on one side of a garden 
path; on the other side of the path were two isolated suckers, 
both of which at this time showed no signs of Oidium. On one of 
these, conidia taken from the rose were sown, and the sucker cov- 
ered over with a bell-jar. The next day it was found that this 
sucker was slightly attacked by an Ozdium, which in the course of 
a few days spread and showed itself on most of the leaves at the 
apex of the sucker. During the whole time, the adjacent sucker, 
left untouched and uncovered, remained free from any Ozdzum. 
It might readily have been assumed that we had here the proof of 
the passing of an Ozdium from one species of host-plant to another, 
but a microscopic examination showed that such was not the case. _ 
The shape of the conidia on the raspberry plants agreed exactly Fi 
with that of the conidia of Sphaerotheca humuli (this species is re- 
corded on the raspberry by Burrill in Ellis and Everh., N. Amer. — 
Pyrenomycetes), and differed from that of the conidia on the 
rose (S. pannosa) in shape and size. The difference between the : 
conidia of S. humuli and S. pannosa I have elsewhere pointed out 
(71). On examining the Ozdium which appeared on the raspberry | 
sucker experimented upon, the conidia were found to agree in shape 2 
with those of S. humuli and not of S. pannosa. It might be sug- 4 
gested, of course, that the difference in shape was due to the in- 
fluence of a different species of host-plant on the same species of : 
fungus, but in the face of repeated experiments (made in a garden 
where no raspberry-Ozdium occurred) in which it was found that — 
conidia taken from the rose and sown on raspberry suckers inva 
riably failed to produce any infection, we are forced to conclude 
that in the first experiment mentioned above the raspberry sucke 
