[Vor. 4 
100 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
ance to the growth of fungous mycelia, whether resinous or 
non-resinous. 
Von Schrenk (’01), in connection with the description of the 
decay of Robinia Pseudacacia produced by Fomes rimosus, 
says: “Тһе manner in which fungus hyphae spread through a 
piece of timber is determined to some extent by the structure 
of the timber. Wood which has large vessels, prominent 
medullary rays, resin channels, or the wood elements of which 
are large-lumened and thin-walled, will be penetrated through- 
‘out its entire mass more readily than wood where those nat- 
ural channels are absent, or which has short, thick-walled ele- 
ments. . . . Growth directly through a solid mass of wood 
rarely takes place, and when it does so it is a very slow 
process." Practically the same idea is conveyed by Buller 
(706) and Bayliss (208). 
On the relative decay in summer wood and spring wood 
Falck (709) says that in cultures of Lenzites spp. which attack 
coniferous wood, the culture blocks show spots of incipient 
decay in two or three months. These spots occur in the spring 
wood, and then with an increase of the incubation period may 
spread to the summer wood or may not, although the whole 
block is covered with the weft of mycelium. The spring wood 
is thus destroyed more readily than the summer wood. Не 
noticed this especially in cultures on blocks of Pinus sylvestris 
where the summer wood appeared to be fully intact, while the 
layers of spring wood had become disintegrated and upon dry- 
ing cracked into cubes (shown in his pl. IV, fig. 2). This same 
deseription of the decay and the relation of summer wood and 
spring wood to resistance to attack by Lenzites saepiaria is 
reported by Spaulding (’11, p. 21). 
The idea previously held throughout the literature, and 
likewise the result of experience, has been that the sap-wood 
is more readily attacked by fungi than the heart-wood because 
of the richer store of available food material in the former. 
On the other hand, the relative durability of the sap-wood and 
heart-wood depends entirely upon the decay-producing or- 
ganism and the species of wood attacked. For instance, some 
fungi will destroy the heart-wood and leave the sap-wood 
