408 



COMPARATIVE MORPHOLOGY OF FUNGI 



forms they are differentiated into numerous layers of tissue; in many 

 genera they are permeated by latex and fat-containing ducts, which are 

 elongate, branched, non-septate, labyrinthiform, anastomosing hyphae of 

 variable thickness. These ducts arise as branches of mycelial threads 

 and contain within a multinuclear, vacuolate cell, milky or colored emul- 

 sion or a hyaline sap which colors on exposure to light or possesses other 

 characteristic properties. Occasionally some of the branches rise from 

 the subhymenium between the basidia (Fig. 270) and end on the upper 

 surface of the hymenium (Fayod, 1889; Istvanffi and Johan-Olsen, 1887, 

 Istvanffi, 1896). 



In the simplest case, the fructification represents a more or less thick 

 hyphal mat which lies on the under side of the substrate, grows radially in 



an umlimited manner, bears the hyme- 

 nium on the lower side and differentiates 

 new young hyphal and basidial elements 

 at its periphery (Fig. 380). Fructifica- 

 tions of this type are called resupinate. 

 Often they persist and renew their hyme- 

 nium in every subsequent period of growth 

 on the same surface, so that they finally 

 develop to a thick crust formed by annual 

 layers. 



The development from these resupi- 

 nate crusts has proceeded in two direc- 

 tions, one mainly hypogaeous, the other 

 epigaeous. In the hypogaeous types, the 

 fructification becomes tuberiform and is 

 differentiated into a firm rind or peridium, 

 and a fertile interior which develops later into a basidia-bearing tissue, 

 the gleba (Fig. 314). In the higher groups, Gasteromycetes, the gleba 

 is freed from its surrounding peridium and elevated by a special 

 structure. 



In the epigaeous types, the crust form is retained; but in these the 

 hymenium continues to show a tendency to develop underneath. If 

 for example, the crust spreads over the surface of a horizontal substrate, 

 it generally remains sterile on the upper surface, raises the margin from 

 the substrate and forms the hymenium on the lower surfaces of these 

 margins. If, on the other hand, the mycelium lies on a vertical substrate, 

 occasionally the hymenium may form on the vertical surface; generally 

 it develops horizontally in zones forming characteristic brackets which 

 bear the hymenium only on the lower side (Fig. 291). 



Doubtless the number of factors which can have favored the placing 

 of the hymenium on the lower side is very great. The hymenia are 

 protected from rain and dew, from falling leaves and from undesirable 



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Fig. 270. — Corticium seriate. 

 Latex vessels penetrating hymenium 

 from below. ( X 150; after Istvanffi, 

 1896.) 



