i6o 



REPRODUCTION 



i. DISCOLICHENS 



a. CARPOGONIA OF GELATINOUS LICHENS. Stahl's 1 work on various 

 Collemaceae followed on the same lines as that of Fuisting. The first species 

 selected by him for examination, Collema (Leptogium) microphyllum, is a 

 gelatinous lichen which grows on old trunks of poplars and willows. It has 

 a small olive-green thallus which, in autumn, is crowded with apothecia; 

 the spermogones or pycnidia appear as minute reddish points on the edge of 

 the thallus. Within the thallus, and midway between the upper and lower 

 surface, there arises, as a branch from a vegetative hypha, a many-septate 

 filament coiled in spiral form at the base, with the free end growing upwards 

 and projecting a short distance above the surface and occasionally forked 

 (Fig. 91). The tip-cell is slightly swollen and covered with a mucilaginous 



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Fig. 91. Collema microphyllum Ach. Vertical section of 

 thallus. a, carpogonium ; b, trichogyne. x 350 (after 

 Stahl). 



coat continuous with the mucilage of the thallus. The whole structure, 

 characterized by the larger size and by the richer contents of its cells, was 

 regarded by Stahl as a carpogonium, the coiled base representing the asco- 

 gonium, the upright hypha functioning as the receptive organ or trichogyne, 

 comparable to that of the Florideae. The spermatia, which mature at this 

 early stage of carpogonial development, are expelled from a neighbouring 

 spermogonium on the addition of moisture and easily reach the protruding 

 trichogyne. They adhere to the mucilaginous wall of the end-cell, and, in 

 two or three instances, Stahl found that copulation had taken place. As the 

 affixed spermatium was empty, he concluded that the contents had passed 

 over into the trichogyne, and that the nucleus had travelled down to the 

 ascogonium. Certain degenerative changes that followed seemed to confirm 



1 Stahl 1877. 



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