Tlie Canl-ei' of the Larch. 
309 
bark, canker is originated. T\Tieu the fruits are ripe and the 
spores are discharged, the air is filled with them. They are so 
microscopic that the eye cannot detect them, yet each spore is 
able under suitable conditions to germi- 
FiG. 7.— Section tliroii?h two fruits of the fnngus, Fig. s.— Spore-bearing sacs 
maguified 20 times. ' of tl'e fungus, magnified 
400 times. 
the examination of a very large series of recently attacked 
larches does not confirm this view. It appears that the. spore 
germinates on the surface of the bark, but it is possible that 
it may fall or be washed into a crack. In the fii'st stage of 
its life it is dependent on the external moisture. Should 
the atmosphere be dry, and should there be no water on the 
bark, the spore could not germinate, and myriads of spores 
continually perish in this manner. But if it obtains the very 
little supply of water needed, the spore sends out a small 
thread wliich pushes its way into the bark, and having got 
hold of the bark it is no longer affected by external dryness 
or moisture. It obtains all it needs fi-om the living juices 
of the tree. The numerous cases examined, especiallj- in veiy 
young trees just attacked, furnish no evidence that the fungus 
can infect the larch only through a wound or injury. The 
bark in such young trees is found to be unbroken. This 
fungus has the same power as the potato fungus of pene- 
trating the protective covering of the plant, but in this case it 
