526 MINNESOTA BOTANICAL STUDIES. 
second collection was placed in a one per cent. solution of 
chromic acid, from which after twenty-four hours it was trans- 
ferred to water and after thorough washing was carried by easy 
stages into seventy per cent. alcohol. 
Methods.—The material for study was, with a few excep- 
tions, dehydrated, imbedded in paraffin, and cut with a Minot 
microtome, carried down to fifty per cent. alcohol, stained in a 
fifty per cent. alcohol saturated solution of Bismarck brown, 
transferred into pure xylol and permanently mounted in Canada 
balsam. Some of the small portions of the mycelium and 
younger stages in the development of the sporophore were first 
stained zz toto, and either mounted directly in formalin water 
and sealed or transferred to paraffin and cut and stained again 
if necessary. The pre-staining method proved very effectual 
and was of great help in guarding against the loss of very small 
bodies, and aided in the imbedding process. Numerous other 
staining methods were tried, but none gave as good result for 
structural study as the one outlined. 
The vegetative tract consists of a complex weft of mycelial 
strands, which vary in size from something less than one-tenth 
of a millimeter in diameter up to two millimeters or more. 
The complexity of the weft is greatly augmented by the copi- 
ous branching of the strands and not uncommonly crossing 
strands become more or less fused together. Some of the 
larger strands have a length of one meter or more, and often 
continue with unvarying diameter for forty or fifty centimeters. 
The larger proportion of the mycelium is found near the 
surface of the soil where it is covered with leaf mould and may 
be found to some extent in the leaf mould itself. Some of it, 
however, runs to a considerable depth in the soil, but without 
diminishing in size or ending there as would a root of a higher 
plant. Invariably, strands found at the greatest depth of twenty 
to thirty centimeters could be traced to the surface in both di- 
rections. Branching seems to be less frequent on the strands 
found deep in the soil, and it was not possible to locate in any 
case what seemed to be the definite center of growth. 
Each mycelial strand is composed of two general areas: the 
central and the peripheral. In the very small threads the cen- 
tral area (Fig. 9, B) consists of a few large hyphe, very long 
in proportion to their diameters, aud without very definitely 
marked cross-septa. Their general direction is, of course, 
