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A DISEASE OF THE BLACK LOCUST. 31 
tum is dead material in the ordinary sense of the term, 
for the live part of a tree, as determined by protoplastic 
cell contents, or their products, starches and oils, extends 
inward fromthe bark but a short distance (in the black locust 
the outermost 15-25 annual rings may be considered alive ) 
differing with the individual and the tree. Hence these 
fungi are not parasites. As saprophytes, they must be con- 
sidered such in a special sense, for although they grow 
ona dead substratum they nevertheless are unable to do 
so except under very special conditions. The fungi which 
Tubeuf * includes under hemisaprophytes differ from 
such a form as Polyporus rimosus in that they frequently 
grow and fructify on dead wood, at least with greater readi- 
ness than this fungus. 
EXPLANATION OF PLATES. 
Plate 1. — Cross-section of the trunk of a living black locust (Robinia 
Pseudacacia) cut at a height of 23 feet from the ground. The heartwood 
has been destroyed by the mycelium of the Polyporus rimosus; a sporo- 
phore of the latter appears at the one end of the section, (about } natural 
size). 
Plate 2.— Polyporus rimosus, growing on a living black locust 
(Robinia Pseudacacia), (about } natural size). 
Plate 3. — A transverse section of much decayed wood of the black 
locust showing the gradual manner in which the wood is being destroyed 
by the mycelium of Polyporus rimosus: m, medullary rays; v, large vessel. 
* Tubeuf, Carl Freiherr von. Pflanzenkrankheiten. 8. 1895. 
