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 in 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, .Z?) consists of a few large hypha?, very long 

 in proportion to their diameters, aud without very definitely 

 marked cross-septa. Their general direction is, of course, 



