Humphrey: Tests on Durability of Greenheart 209 
sapwood proved far less resistant. Lensites sepiaria proved the 
most active organism, producing a loss in dry weight of 37 per 
cent. Merulins lachrymans stands next with a loss of 26 per 
cent. Six other fungi produced losses ranging from 10 to 25 
per cent. The wood remained practically immune to only three 
of the twenty-three fungi used. 
The fact that the sapwood is more susceptible to decay than 
the heartwood meets our natural expectations, as this is the rule 
with timbers in which the heart and sapwood are differentiated. 
The point to be kept in mind is that the sapwood, being so 
much less resistant to decay than the heart, should be carefully 
considered in timber specifications which call for the best quality 
of durable material. Not alone is the sapwood moderately sus- 
ceptible to the attacks of fungi, but it is also reported to be more 
readily attacked by marine borers, and hence is said to be less 
valuable for wharf construction. 
Office of Investigations in Forest Pathology, 
Bureau of Plant Industry, 
Madison, Wisconsin. 
Description of Plate CLXII 
Fig. I. Cultures in large tubes of six species of fungi, showing method 
of testing. Each tube contains a greenheart block surrounded 
by easily rotted culture blocks. After i year. 
Fig. 2. Greenheart test blocks, heartwood above ; sapwood, with wane, 
below. 
Fig. 3. Greenheart block and beech culture blocks matted together by a 
heavy growth of mycelium at end of the test period. Stereum 
fasciatum above,- Polystictus hirsutus below. 
Fig. 4. Photomicrograph of transverse section of greenheart wood. Note 
the compact structure and tyloses partially filling the ducts. 
(By courtesy U. S. Forest Service.) 
Fig. s. Radial section of greenheart wood. (Courtesy of U. S. Forest 
Service.) 
Fig. 6. Tangential section of same. (Courtesy U. S. Forest Service.) 
