52 



The Naturalist. 



Local conditions favourable to the growth of cryptogamic vegeta- 

 tion are — moisture, the presence of decaying vegetable matter, and 

 the absence of undue competition of the higher plants. These 

 conditions are met with on wet sandy heaths, and in moist woods, 

 hence such places usually abound with mosses, lichens, and fungi. 



Mosses and lichens, as I have said, shrivel up when dry, and revive 

 with moisture ; when dry, all vital processes are of course suspended, 

 consequently the more frequent or constant the supply of water, the 

 more luxuriant, cotteris paribus, will be the growth. The decaying 

 vegetable matter no doubt furnishes them with an ample supply of 

 carbonic acid. Mosses and lichens " object to smoke," not on account 

 of the carbonic acid, but of the sulphuric and hydrochloric acids 

 which it contains. They will always be found much more plentiful 

 on the roofs of farm buildings than on those of dwelling-houses ; in 

 one case they are poisoned by the soot and smoke, in the other they 

 are nourishei by the decaying dust from straw, &c., which lodges on 

 the roof. Old thatch roofs are especially favourite places. 



Mosses are usually the first vegetation which springs up on new 

 soil, as freshly exposed rock surfaces sand and mortar, from which 

 the seeds of other weeds are absent, and they serve an important use 

 in such situations by forming the first thin layer of vegetable mould, 

 in which plants of a higher grade following them can take root. The 

 mosses which first appear in such situations are minute annual kinds, 

 which appear in abundance the first year, but soon die out, either 

 from requiring a fresh soil year by year, or through being stifled by 

 the growth of more robust plants. 



Some mosses exhibit tastes for which there is no accounting : thus 

 one genus, Splachnum, is only found on decaying animal substances 

 in mountainous situations ; the hat of a traveller lost on the Alps has 

 been found covered with one of these mosses. A very common moss, 

 F/iiiaria hygrometrka, loves anything that has been burnt, and is 

 abundant on cinder paths, burnt heathy ground, brick walls, and mortar. 

 I never but once found it on a tree, and that had been charred. 

 These idiosyncrasies are still more marked in the case of the fungi ; 

 a great number of the smaller species have their own special pabulum, 

 upon the presence or absence of which their occurrence depends, 

 rather than upon geographical and climatic conditions. Many of the 

 parasitic leaf fungi grow only on the leaves of a single species, or 

 species belonging to one genus : the habitats of some other fungi are 

 still more curious ; thus, Onygena equina grows on decaying hoofs of 



