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RESEARCHES ON FUNGI 



great as possible. Evidently, with the form of the wedge given, the 

 area of the lateral sides cannot be increased, but the volume can be 

 diminished by reducing the wedges in depth and increasing their 



H 



B 



H 



B 



FIG. 138. Diagrams to illustrate the relation of gill-depth to gill-surface and gill- 

 volume. Left, a steel wedge in cross -section, with replacement by two, four, 

 or eight wedges. Right, a gill in cross-section, with replacement by two, four, 

 or eight gills. The eight small gills have much less surface than the eight 

 small wedges. 



number. One would therefore make the wedges as small as possible. 

 The limit would be determined by human skill : it would be found 

 that wedges could not be made less than a certain depth and yet 

 retain their true symmetry. 



Instead of a wedge of steel let us now consider a gill (Fig. 138, 

 A'B'C'). A gill is wedge-shaped, but differs from the steel wedges 

 already discussed in that its sides are slightly convex and in that it 



