A TOADSTOOL—ITS FUNCTION AND FORM 9
new gill. The wasted areas are shown stippled in Fig. 5
Sector B.
It is clear that the available space could be much more
efficiently used if cross partitions (anastomoses) covered by
hymenium and the safe distance apart were formed (Fig. 5
Sector C). This arrangement is well on the way to the poly-
pore habit. The actual extent of the hymenium in this is 263
units as compared with 102 units in the quadrant with gills.
In quadrant I) the space has been filled (experimentally not
mathematically) by circular pores 1 unit i.e., the safe distance
in diameter. Here again the extent of the hymenium (185
units) is much greater than in the case of gills and no doubt
this figure could be increased somewhat by closer packing of
the circles.
Fig. 5. Diagram of the various ways in which the under surface of a toad-
stool may be partitioned by hymenial surfaces. For further explanation see
text.
The point I am getting at is this : the polypore arrangement is
a more efficient method of using the space below the cap than
a system of gills. We may expect, therefore, an evolutionary