150 ARM1LLARIA MELLEA, 



horizontally for a short distance and then dropped by their 

 own weight between the gills. For this purpose it is neces- 

 sary that the gills should be vertical, and -this orientation 

 is secured by a triple action (Buller, 1909). The stipe is 

 vertical, the pileus adjusts itself to a horizontal position, 

 and finally the gills place themselves vertically. 



A section of the gills stained with iodine disclose some 

 interesting facts with regard to the distribution of glycogen, 

 the principal reserve carbohydrate of the 

 fungus. In young basidia glycogen is 

 fairly generally distributed ; but, as they 

 get older, part of the glycogen is passed 

 into the spores, and the rest is left as a 

 drop at the upper end of the basidium. 

 FIG. 62. Hymenial Basidia which have lost all their spores 

 layer of Armillaria s till contain this drop of glycogen, and 

 mdlea (x420). . . , ,. 



its function is probably to provide the 



osmotic pressure necessary for the discharge of the spores 

 (see p. 104). The ripe spores measure about 9X 6/x, and are 

 somewhat reniform. 



Rhizomorphs. Armillaria mellea has a more specialized 

 vegetative system than any other known fungus. In 

 a nutrient medium such as a rotten stump, and especially 

 in the space between the wood and the bark of dead trees, 

 it makes a reticulated mass of somewhat thick strands or 

 rhizomorphs, each flattened thread of which resembles 

 a black leather boot-lace (figs. 63 and 64). From points 

 beneath the soil these rhizomorphs send out branches into 

 the earth, which are of a somewhat different type, being 

 round in section instead of flat, and having fewer branches. 

 Both types of rhizomorphs were known long before they 

 were associated with any particular fructifications, and 

 they long went by the name Rhizomorpha subcorticalis and 

 Rh. subterranea?- Persoon, respectively. It was not even 

 determined that the two forms belonged to the same species 



1 Sowerby, vol. iii, 1803, figures five species of Rhizomorpha, two of 

 which are certainly Eh. subterranea. The others are doubtful, but none 

 resembles Rh. subcorticalis. 



