Humphrey: Tests on Durability of Greenheart 205 
The great durability of the wood has been mainly attributed 
to two factors, (i) the presence of the tyloses, which stuff the 
vessels and thus render them more difficult of penetration by 
fungus mycelium, and (2) the presence in the wood of certain 
alkaloids which may exert a preservative effect. 
At least four alkaloids have been extracted from the wood and 
bark, among which may be mentioned bebeerine- (or biberine) of 
the formula CigHjiOjN, and nectandrine, CjoHjgO^N. The 
former is said to be commercially exploited as a substitute for 
cinchona. It contains a methoxyl group, a phenolic hydroxyl 
group and a NCHj group. 
The toxicity to fungi of these alkaloidal extracts from green- 
heart has not yet been determined by the writer, but it is the 
plan to make such tests later, in an effort to throw further light 
on the durability of this remarkable wood. 
During 1913-14 the writer conducted a series of durability tests 
on both the heartwood and sapwood of greenheart timber. The 
material was sent to the Forest Products Laboratory, Madison, 
Wisconsin, from British Guiana for test purposes. The ship- 
ment consisted of a 13 by 13 inch square-hewn timber, upon 
which the bark was still adhering to the corners in strips an inch 
to an inch and a half wide. The sapwood was about two and a 
half inches thick, being largely confined to the corners, it being 
hewn away at the center of the faces. 
Test blocks ^ by by 2 inches long were sawed out from 
near the center to secure good heart material, while the sapwood 
specimens were cut from near the circumference at the corners, 
in many instances representing the extreme outer surface, and 
hence less than normal size on account of the wane (Plate 162, 
fig. 2). 
Each block was tested singly in a large test tube i^ inches in 
diameter and 9 inches long, the sapwood and heartwood being 
tested against the same organisms. Seventy tube cultures were 
originally planned, using 35 species of wood-destroying fungi 
common to the United States, but certain failures incident to the 
experiment reduced this number somewhat. 
’ Henry, T. A . The plant alkaloids, pp. 414, 415. 1913. 
