570 



COMPARATIVE MORPHOLOGY OF FUNGI 



swells greatly and the dicaryon fuses, forming a single diploid nucleus. 

 The zeugites elongate, forming the basidia. Because of the mutual 

 pressure under the epidermis, they are flattened next each other and form 

 a compact layer which is imbedded in a gel secreted by the membranes. 

 In some species the basidia are thickened at the tip. This is primarily 

 a biological adaptation, since the tips must rupture the epidermis by 

 their pressure. After a time the basidia divide, as in Auricularia, into 



Fig. 383. — 1. Coleosporium Sonchi-arvensis. Hymenium. 2. Thekopsora areolata. 

 Tclium. 3. Melampsora Helioscopiae. Telium. (1 X 270; 2, 3 X 340; after Sappin- 

 Trouffy, 1896.) 



four cells, each cutting off a basidiospore and raising it above the ruptured 

 epidermis on a long sterigma. 



In Gallowaya pinicola (B. O. Dodge, 1925) there is very little inter- 

 twining of hyphae as a preliminary to the formation of the telial sorus. 

 The hyphae grow out through the mesophyll and form a palisade of 

 chains of four or five uninucleated cells. The terminal cells form the 

 peridium as in the covered type of aecidium or primary covered uredi- 

 nium. Soon after the epidermis is ruptured cell fusions occur between 



