10 BOTANICAL GAZETTE [JANUAR 
mingled in the substratum, and that any particular hymenial 
layer is made up of fertile branches from different mycelia. 
Their ability to combine into the even homogeneous film 
extending over many square centimeters would be wholly du 
to their similar environment and their mutual interaction, an 
not to any unity of origin, since each mycelium must b 
regarded as an independent plant. 
It is plain that this conception of the Hypochnus hymenium ~ 
as a compound having no strict individuality is of great impor 
paring them with the fruit bodies of the Ascomycetes, which arise ; 
typically at least as units from the cell or cells of a sexual appa 
ratus, so far as their fertile ascus-bearing hyphae are concerned, — 
it occurs, however, is a still further point of difference between 
the Ascomycetes and the Basidiomycetes. The former neve! 
show such secondary hymenia developed on the surface of old 
-hymenia. The ascogenous hyphae show frequently a protracted, 
but none the less ultimately a definitely limited, growth, result: 
ing ina characteristic fruit body, the ascocarp; while the merely 
vegetative hyphae which bear the basidia may prolong and 
repeat at intervals the development of new hymenial layers. _ 
| The stromata of Diaporthe, and other similar types which — 
may show more or less secondary growth, are not ascocarps, but 
vegetative mycelia bearing ascocarps imbedded in their sub- 
stance (18). 
