THE FUNGI 251 



gonium. Its lower end, which usually forms a coil, is 

 embedded in the medullary tissue of the thallus, while 

 the upper portion projects beyond the surface of the 

 cortex, terminating in a long cell, the trichogyne (see Fig. 

 104). The trichogyne has a gelatinous cell- wall, to 

 which numerous spermatia are found adhering. There is 

 reason to believe that only those carpogonia, of which the 

 trichogynes have been fertilised by spermatia, develop 

 into ascus-fruits. The asci spring from cells of the coil 

 (ascogonia), while the paraphyses arise lower down. It 

 appears, then, that in these Lichens there is a sexual 

 process resembling that in the Floridese and in certain 

 Fungi. The details of fertilisation, however, still re- 

 quire to be worked out. In some cases, on the other 

 hand, the spermatia have been observed to germinate, 

 so their function as male cells seems not to be constant 

 throughout the group. The illustrations (Figs. 102-104) 

 are taken from a Lichen (Physcia, pulverulenta), closely 

 allied to our type. 



The ascospores, as we have seen, reproduce only the 

 fungal element of the Lichen ; they must meet with 

 algal cells in order to form a perfect Lichen-thallus. 

 In many members of the group, however, though not 

 in our type, there is a special provision for the re- 

 production of the compound organism as a whole. In 

 these Lichens we find some of the apothecia replaced 

 by patches of a powdery substance, each grain of the 

 powder consisting of a few algal cells invested by fungal 

 hyphse. These little groups become isolated, and are 

 dispersed by the wind or rain, or by the agency of 

 insects. They are called soredia, and serve to reproduce 

 at once the algal and fungal constituents of the Lichen. 

 The group of soredia is here homologous with an 



