328 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
radially at their outer end. They vary in length from about 1 to 
10 mm. and up to 5 mm. in width at the tip. 
They are clothed with a loose outgrowth of hyphae from their 
earliest appearance. These hyphae are thick-walled and no 
branching was observed. Clamp connections or cross-walls were 
not found in these superficial hyphae. 
Transverse vertical sections of young buttons show a dense 
homogeneous mass of intertwined hyphae developing parallel 
with the elongating axis of the primordium. The hyphae show 
conspicuous clamp connections. The carpophore primordia are of 
leathery consistency and show no evident differentiation until the 
appearance of the hymenium primordium. 
THE HYMENIUM 
In young buttons the first appearance of the fruiting layer is 
just below the upper end. It consists of a growth of densely 
staining hyphae. Horizontal sections show this first structure or 
plectenchyma of hyphae centrally located. With further growth 
of the carpophore primordia they become somewhat elliptical in 
outline. The individual hyphae now become oriented, their free 
ends converging towards the center of the mass. 
The first gill cavity is formed in this hymenium primordium. 
The oldest primordia are in the central part and the youngest 
towards the sides, showing the order of their formation (TEXT- 
FIG. A, NO. 2). 
The whole carpophore enlarges and as result of growth ten- 
sions the gill cavities appear in the center of these primordia of the 
hymenium. The gill cavities are lined from the first by a palisade 
layer. The palisade layer is increased by the intercalary addition 
of new elements with the further increase in size of the gill cavity. 
The elongated cells composing the palisade layer stain deeply and 
appear to arise as a system of short branches from the subjacent 
hyphae which are to form the trama. 
The gill cavities thus represent from the first the space between 
the adjacent halves of two lamellae. The hymenia are oldest 
toward the base and less undifferentiated toward the tip of the 
carpophore. 
In two instances gill cavities were observed developing in the 
