150 ARMILLARIA MELLEA, 
horizontally for a short distance and then drepped 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. 
Fic. 62.—Hymenial Basidia which have lost all their spores 
layer of Armillaria still contain this drop of glycogen, and 
ee Caen its function is sarcbably to provide the 
osmotic pressure necessary for the discharge of the spores 
(see p. 104). The ripe spores measure about 9X 6n, 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 Rh. subterranea. The others are doubtful, but none 
resembles Rh. subcorticalis, 
