1914) 
VON SCHRENK— TWO TRUNK DISEASES OF MESQUITE 245 
part. The decayed wood isvery brittle, but still remains fibrous, 
that is, it does not crumble into powder like charcoal. It splits 
like sound wood, but is spongy and soft. The wood of the 
mesquite is very hard and heavy, a cubic foot weighing 47.69 
pounds when absolutely dry. It consists of numerous, distinct 
medullary rays, and distinct but irregularly distributed bands 
of very thick-walled wood fibers, between which occurs a 
thinner-celled wood parenchyma. In the heart-wood the 
lumina of the cells of the latter tissue are usually completely 
filled with a yellow-brown substance, largely composed of tan- 
nin. McMurtree (8) found tannic acid in large quantities in 
mesquite wood, 6.21 per cent in the heart-wood, 0.5 per cent in 
the sap-wood, and 0.5 per cent in the bark. Besides tannin 
he found of materials other than tannin, insoluble in water but 
extracted by ether, 0.6 per cent in the heart-wood, 6.7 per cent in 
the sap-wood, and 1.84 per cent in the bark. A considerable 
number of large, open ducts are found in the early part of each 
wood ring. These also are filled with a yellow-brown substance 
similar to that found in the wood parenchyma. 
The fine, colorless mycelium of the fungus spreads throughout 
the wood substance. Unlike Polyporus rimosus in locust wood 
(10), the fungus does not destroy the wood as a whole, but 
attacks only the heavily lignified groups of wood fibers. "These 
are wholly destroyed, leaving holes or gaps between the vessels 
and wood parenchyma. The dissolution of the wood fibers evi- 
dently proceeds with great rapidity, starting with the secondary 
thickening of each cell. The cells disappear entirely, and in 
advanced stages of decay small masses of mycelium are the only 
evidence of their former presence. Although the wood paren- 
chyma and the vessels are filled with hyphe, they resist destruc- 
tion almost completely,—a fact which may be connected with 
the very high tannin content of both of these tissues. The 
recent results of Wehmer (11), who found that for certain 
species of fungi tannin exerts a retarding influence on develop- 
ment, and the similar findings of Knudson (7), and of Cook and 
Taubenhaus (3), who state that “tannin has a tendency to 
retard or inhibit the growth of fungi," and that “the parasitic 
forms are more sensitive to the action of tannin than the sapro- 
phytic forms,” lend support to this idea. Cook and Taubenhaus 
