1896] A RUST AND LEAF CASTING OF PINE LEAVES 445 
months after infection, the fungus is found in the condition 
already described. A month or six weeks later it again pro- 
duces spores, thus completing its cycle of development in one 
year. 
CASTING OF THE LEAVES AND ITS CAUSE. 
As already pointed out, we have in the case of the Coleospor- 
ium a fungus producing first purely local injuries, which later 
tesult in the death and casting of the leaves. The phenomena 
involved in this process may now be considered. An examina- 
tion of the diseased leaves soon after the sori collapse shows 
that the conductive tissue has not been injured at all, the endo- 
dermis being intact and the fibro-vascular bundles abundantly 
able to conduct water. That they do this is evident from the 
fact that, even though the mesophyll invaded by the fungus ss 
brown and shriveled, the tip of the leaf above this part remains 
green for a considerable time. In the tissue where the fungus 
has been at work there are large rifts which extend unbrokenly 
tothe endodermis. The cell contents of the mesophyll region 
immediately below the part attacked by the Coleosporium, and 
Where there is no mycelium at-all, are broken up, showing that 
changes are taking place which are not directly attributable to 
the fungus. These changes are manifested externally by the 
Yellowing, already described,: which gradually extends lated 
ward until both needles are involved. Even before this the 
“eparative layer begins to form and in a week or ten aye ee 
the Pair of needles fall. Of course, the fungus itself is the pri- 
mary cause of the leaf fall, but that it acts only as 4 Powe! - 
et other causes at work was early shown by cutting see - 
affected portions of the leaves. In every instance this treat- 
Ment caused the leaves to remain on the tree and perform their 
functions in a normal manner until death came from old age- 
In all Cases, however, it was found necessary to make the i 
through normal green tissues, @. ¢., below the poin 
yellowing showed. If only one needle was 
we 
Partly yellow and the cut was made through the discolored po 
