10 THE ESSEX NATURALIST
pressure from gills towards pores, if we suppose that the pro-
duction of the maximum number of spores for the minimum
expenditure of fungal tissue is an advantage in the struggle
for existence.
It should, however, be noted that in passing from the gill to
the pore the power of fine adjustment of the gills is lost. Bach
gill of an agaric is free to move, but the pores of a Boletus are
too closely knit together to permit individual movement of the
pores. Possibly the very stout stipes of Boletus spp. as com-
pared with those of other fleshy agarics are connected with the
lack of power of fine hymenial adjustment.
If there is evolutionary pressure from agaric towards poly-
pore, we might expect that this step would have been taken on
more than one occasion. Largely thanks to the labours of
modern French mycologists, we have come to realize that
neither the Agaricaceae (gill-bearing fungi) nor the Poly-
poraceae (pore-fungi) of Elias Fries can be regarded as
Fig. 6. Sectors of under surface of cap in a number of fungi closely
related to Mycena (the condition in that genus being shown diagrammatic-ally
in A) B. Mycenoporella clypeata; C, Poromycena manipularis; D, Phlebomycena
madecassensis; E, Phacomycena aureophylla. B, C, D, and E after Heim.