BIOLOGY OF COLLYBIA VELUTIPES. 157 
surface, carrying out with them fragments of disintegrated 
tracheids and vessels *. These rhizomorphs are far simpler in 
structure than those of Agaricus melleus, for they consist merely 
of bundles of shortly septate hyph:e, unenclosed by any specialized 
cortical layer and without a definite growing-point. In much 
attacked parts of the wood the hyphe are often of a rich brown 
colour, re:embling that of the sporophore; but on carefully 
following them, the colouring is found to be restricted to small 
areas. The colour of the sporophore is not therefore due to 
this colouring-matter being directly transported to it. In the 
medullary rays the hyphæ often grow to a great size. A similar 
rank development of hyphe is described as occurring in Polyporus 
borealis, Fr., among other wood-destroying fungi T. 
The first noticeable action of the mycelium is to destroy the 
starch contents of the medullary rays, and it is not until the 
infeetions are three or four weeks old that the characteristic 
action becomes evident. The thickening-layers of the tracheids 
and fibres are then seen in transverse sections to be pitted in 
many places, either as far as the first thickening-layer, or right 
through to the middle lamella (Pl. 4. fig. 15). In longitudinal 
sections these pits are found to be grooves corroded out by the 
action of the hyphs, which thus leave a map of their path 
(Pl.4.fig. 16). It frequently happens that these grooves lead 
directly to small irregular holes in the walls of the elements, show- 
ing where the hyphe have turned to pass through a pit which has 
subsequently been enlarged. The action of the hyphe is thus a 
* Cf. Eichelbaum, Bot. Centr. 1886, xxvi. p. 205. 
t Hartig, Zersetzungerscheinungen des Holzes, p. 56. 
+ The view taken here with regard to the constitution of the walls of the 
wood elements is, that the middle lamella is primarily composed of cellulose or 
pectates, which during the process of iignification is impreguated with a substance 
or with substances known collectively as lignin!. The thickening-layers consist 
of cellulose, again impregnated, but to a lesser extent, with lignin. The staining- 
reactions for the presence of vanillin, coniferin, and pectates failed to give any 
satisfactory results when employed during this research. 
This view is consistent with the results given by the employment of 
Wisselingh's cellulose test ?, and with Hoffmeister’s method of analysis®. In 
the former the glycerine exerts a gradual solvent action on the lignin, dis- 
solving it completely from the thickening-layers, before dissolving it altogether 
from the middle lamella. 
! Cf. Tollen's Handbuch der Kohlenhydrate, vol. ii. p. 270. 
? Wisselingh, Pringsh. Jahrb. 1898, p. 619. See also p. 158 of present paper. 
3 Hoffmeister, Landwirthschaftlichen Versuchs-Stat. 1898, p. 347. 
