ANATOMY OF FUNGI 43 



above, fixed by a more or less broad base, and growing at 

 right angles to the matrix, the sporophore is said to be 

 dimidiate. This type of sporophore is very commonly 

 seen in species belonging to the Thelephoraceae and the 

 Polyporaceae, when growing on the vertical surface of 

 trunks, posts, etc. A further approach to the truly central 

 stem, as seen in most Agarics, is brought about by the 

 gradual narrowing of the point of attachment of the sporo- 

 phore, at the point where it becomes free from the matrix 

 or support on which it is growing. When this point of 

 attachment is much reduced, the sporophore grows out as 

 a more or less circular or fan-shaped sporophore, supported 

 by a short, narrow, stem-like base, and is described as 

 flabellate. If we imagine the two free margins of the 

 sporophore nearest the stem adhering together, we get the 

 first suggestion of a central stem supporting a pileus, 

 sterile and protective on the upper surface, and bearing the 

 hymenium on its under surface, and pointing towards the 

 ground. The upward growth of the stem, and the down- 

 ward growth of the gills in Agarics, the spines in Jfydnum, 

 etc., are said to be due to negative and positive geotropism 

 respectively. 



In Agarics the margin of the pileus is strongly incurved 

 when young, so that it is in contact with the stem, and the 

 extreme edge is also often inrolled on itself. This is stated 

 by De Bary to be due to epinasty, or the more vigorous 

 growth of its upper surface than that of the lower. At 

 a later stage of growth the pileus gradually expands and 

 changes its original bell-shape for that of an expanded 

 umbrella, or may become plane with the edge more or less 

 upturned. This is due to hyponasty, or the more rapid 

 growth of the under than the upper surface of the pileus. 



