1896] A RUST AND LEAF CASTING OF PINE LEAVES 443 
Usually, however, the sporidium separates from the promycelium 
in about thirty or forty minutes after the partition forms, and 
then almost immediately begins to germinate by sending out 
ashort, thick germ tube. All or nearly all the contents of the 
sporidium flow into the germ tube. Occasionally this tube grows 
out to a considerable length, cutting off a secondary sporidium 
(fig. 76) upon its free end in much the same way that the orig- 
inal was formed. 
After the spore germinates the walls remain turgescent for a 
short time, and then collapse and dry up, the spore in the mean- 
time becoming perfectly colorless. The entire contents of the 
cell seem to be used up in the formation of the promycelium ° 
and the sporidium, and if this is not the case the formation of 
secondary sporidia goes on until there is no protoplasm left. 
Germination as here described takes place in nature only 
When the leaves are wet, the spores themselves seldom if ever 
escaping from the sorus. The sporidia, however, when cut off 
from the promycelia either fall or are washed down to the leaves 
below or to the ground, where they may be found in great 
abundance after a damp or foggy night. In all infection exper- 
iments, which will be referred to later, the sporidia were 
obtained in abundance by placing sterilized Petri dishes under 
the diseased branches confined in a moist chamber. After sev- 
eral hours an abundance of sporidia may be obtained from the 
dishes, 
INFECTION OF THE HOST. 
On Closely examining the diseased trees the spori¢ 
Hund on the young leaves, which at this time are just begin- 
hing to show their tips. The usual place for lodgment is 
between the tips of the two young needles, which at _ 
“a Spores are forming project about 0.33™ above the shea 
Which incloses them. The needles are slightly sp = uae 
an peowing a small drop of water to be seta ree 
Dy Collects in this way drips from the old leaves ae 
teh the Spores and sporidia are being formed. in PP ‘ 
down it Carries the sporidia with it, depositing the lane if 
dia may be 
