i 2 V. H. Blackman — 
surrounded by a moist atmosphere. Those sown in the hanging 
drops germinated after some delay, but most of the tubes 
produced formed no sporidia, but grew to a considerable length in 
the water without showing the least signs of the formation of 
transverse walls. As the tube increased in length the protoplasm 
collected at the apex, the cavity behind being left almost empty. 
A few of the tubes, however, by continued growth reached the 
free air outside the drop, when their growth soon stopped and the 
portion in the air became divided into the usual four sporidia- 
bearing cells. Only a small proportion of the tubes produced in 
the hanging drop succeeded in developing sporidia, and there was 
no evidence that they were positively chemotactic towards oxygen. 
The spores sown in the moist air germinated more readily 
than those in the drop cultures, but the germ-tubes so pro - 
duced were very short and formed sporidia almost immediately, 
so that the promycelium consisted of little more than the four 
sterigma-bearing cells. In pi. I., fig. 4, there is shown a com¬ 
pound teleutospore of Phragmidium rubi, two of the cells of which 
have germinated in a hanging drop. The lower germ-tube has 
reached a very considerable length, but there is no sign of sporidia 
formation; the protoplasm has collected mainly at the apex. 
Many of the germ-tubes were very much longer, but unless they 
reached the air, they never became divided into sporidia-bearing 
cells. In fig. 5 a similar teleutospore is shown, which has germi¬ 
nated in moist air. The promycelium is very short, division into 
four cells has taken place, and the sterigmata are already formed. 1 
It is clear from the two sets of observations that, in the forms 
under consideration, the submerged germ tube or promycelium 
is incapable of sporidia formation, but that its growth in length 
is only limited by the reserve material at its command. Sporidia 
formation however takes place directly the tube reaches the air, and 
if this condition is present from the beginning of germination, 
growth in length is of very short duration and the promycelium 
becomes reduced to little or nothing more than the characteristic 
four cells. 
1 Whether the existence, even in the case of the spores grown in 
moist air, of a small portion of promj'celiiun which forms 
no part of the sporidia-bearing cells (as in fig. 5) is a 
normal phenomenon or is to be explained by the presence 
of a thin layer of water deposited from the air upon the 
spore wall, could not be ascertained. The fact that in the 
figure of P. rubi given by Sappin-Trouffy this stalk-like 
portion is till more reduced, and in the figure of Cronartium 
given by Tulasne (loc. cit.) it seems to be entirely absent, 
would suggest that the latter explanation is the probable 
one. 
