32 



the course of which he remarked that at one time these 

 plants were considered as forming a distinct tribe. Now, 

 however, they were considered by leading cryptogamists to 

 be merely commensals, or partnerships formed between a 

 fungus and an alga. By means of blackboard diagrams the 

 lecturer explained the structure of the lichen-thallus, and the 

 nature of its several strata. Briefly, there were an upper 

 and a lower epidermal layer, consisting of a close aggregation 

 of cells, and to the lower layer rhizines were attached. Be- 

 tween these layers of epidermis were two differing elements : 

 a loose stratum of green cells {gonidid), and below this a 

 medullary layer of hyphse. The gonidia were very similar 

 to the simple alga Protococcus, and the contention of the 

 new school was that these Protococci had been captured by 

 an ascomycetous fungus and held in bondage. By means of 

 their chlorophyll the gonidia were able to manufacture starch 

 from the inorganic material obtained by the rhizines 

 (mycelium), and this starch the other portions of the co- 

 operative organism were enabled to feed upon. Some of the 

 gonidia were pushed out of the thallus from time to time, 

 covered with a slight wisp of hypha (soredia), and had the 

 power to grow into another lichen-thallus, or to increase 

 simply as gonidia. Schwendener and Bornet claimed to 

 have produced lichens by sowing the spores of Parmelia 

 parietina among Protococci, and that wherever the hyphae 

 came into contact with Protococcus, in groups or singly, they 

 attached themselves. Tulasne and De Bary, however, 

 believed that they had detected the growth of gonidia from 

 the hyphse ; Berkeley also believed in this mode of origin 

 for gonidia ; and the lecturer suggested that Protococcus, 

 instead of being a distinct species, might be merely the 

 escaped gonidia from lichens leading a free and independent 

 life. The varieties of the thallus and their habits were next 

 considered ; the phenomena of growth and reproduction ; 

 classification and uses ; and hints on their collection and 

 preservation. Much interest was added to the lecture by the 

 exhibition of a large number of mounted specimens. 



MAY I2th, 1892. 



C. G. Barrett, Esq., F.E.S., President, in the Chair. 



Mr. R. Adkin exhibited specimens of Lepidoptera picked 

 out from a collection made at Rannoch, and remarked that 

 in a limited selection it was impossible to show the whole 

 range of variation. There was nothing of special interest 



