. Comparative morphology of Fungi. Fungi. 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 bet
. Comparative morphology of Fungi. Fungi. 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 margi
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