94 MISSOURI BOTANICAL GARDEN. 
Examples of the first class of disease need not be given; 
the root rot of pines * is an example of the second class, 
and the numerous fungi (and insects) attacking different 
parts of a tree come under the third class. It is particu- 
larly the latter class which Hartig has studied and with 
some of which the present paper is to deal. 
The fungi attacking trees may be divided for convenience 
into such as are strictly parasitic, like the Peridermiums, 
Exoasci, Gymnosporangiums, etc., and such as are not. 
Among the latter class one finds various grades, going from 
the strictly parasitic to the strictly saprophytic forms, 
including the facultative saprophytes (of De Bary) or 
hemiparasites, the true saprophytes, and the facultative 
parasites (De Bary), or hemisaprophytes. Of the fungi 
which attack the trunks of trees, i. e., the wood already 
formed, few are strictly parasitic or hemiparasitic; the 
majority are hemisaprophytes, for although normally 
growing on dead matter they may occasionally become 
truly parasitic. Tubeuft mentions a number of such fungi, 
among them several common in this country, such as 
Trametes Pini, Polyporus fomentarius, Polyporus sul- 
phureus, and others. Trametes Pini may serve as a good 
example. When growing on species of pine, such as Pinus 
palustris, Pinus Strobus, Pinus echinata, it flourishes in 
the heartwood of these trees as a strict saprophyte, i. e., 
on the dead wood. The resinous contents of the living 
wood prevent its becoming parasitic. On the other hand, 
when growing on Abies balsamea or Picea nigra it becomes 
a parasite, growing likewise in the living wood and ulti- 
mately killing the tree. The diseases to be discussed in 
the following are due to hemisaprophytes, as they affect the 
heartwood of the trees and never enter the living parts of 
the trunks. 
* Hartig, R. Zersetzungserscheinungen, etc. 75. 
+ Tubeuf, C. Freiherr von. Diseases of plants 5. (English edit. by 
W.G. Smith. 1897.) 
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