THE VICTORIAN NATURALIST. 117 



that the ascospores of lichens cannot germinate without fresh 

 algae cells. 



De Barry is very confident on this point. He states : — " If the 

 ripe ascospore of the Hchen fungus is placed on a moist sub- 

 stratum, it in most cases puts out germ tubes. These may in 

 some cases form numerous branches, but they always perish after 

 a certain time if they do not encounter suitable algae, even when 

 the germination has taken place on a substance favourable to the 

 nutrition of the lichen. It must be remembered that there are 

 many other algae besides nostocs which are incorporated with 

 fungi to produce lichens. In fact, so many and so various are the 

 combinations that the difference of species depends greatly 

 upon the chemical condition of the substratum and the amount 

 of light and moisture." 



Kerner gives the following evidence upon this point : — "Near 

 the famous castle of Ambras, in Tyrol, there is an octagonal 

 marble column which has been standing in its place for more than 

 200 years, with all its sides exposed to wind and weather. 

 Lichens have settled on all the eight faces. . . . And on this 

 column there are a dozen different species, the germs of which 

 can only have been brought by winds. These species are, 

 however, by no means uniformly disposed. Some prevail on one 

 side and some on another, and a few are confined exclusively to 

 one of the eight faces. Of three species of Amphiloma, one is 

 restricted to the face exposed to the south-west, a second is to be 

 seen on the upper part of the southern face, whilst the third is 

 found on the same face, but close to the ground. On the side 

 with a northern aspect a different genus predominates, whilst the 

 prevailing forms on the north-west face are entirely different from 

 those already mentioned." The symbiosis between fungi and algae 

 in the constitution of lichens is now a well-established fact, and 

 is acknowledged by all botanists. 



The consequence of this partnership is that plants are formed 

 which have a powerful influence in the economy of nature. The 

 fungoid partner not only has the power of closely adhering to the 

 rock, but it can exude acids which reduce the substratum of the 

 rock into powder. This desiccation of rock surface, together with 

 the mass of vegetable matter created by the algai partner, forms 

 the basis of most of the vegetable mould required for the growth 

 first of mosses and ferns, and finally of flowering plants. Thus 

 we see that the partnership of these — some of the lowliest plants 

 in creation — is a mighty factor in clothing the earth with verdure. 



In Crabbe's poem of " The Borough " the following beautiful 

 lines appear, which faithfully describe such a process as it 

 occurs on ruined buildings : — 



" Seeds to our eyes invisible, will find 

 On the rude rock the bed that fits their kind ; 

 There in the rugged soil they safely dwell, 



