MOSSUS AND THEIR WATER-SUPPLY. 479 



other cardinal points in Kant's doctrine ; but am obliged to aban- 

 don the intention. A state of health such that the foregoing 

 pages, commenced in the middle of March, I have been unable 

 to complete till the first week in June, compels me now to desist. 



MOSSES AND THEIR WATER-SUPPLY. 



Bt Pkof. G. HABEELANDT, of Graz. 



THE interest with which botanists regard the mosses is, for 

 various reasons, more lively and more diversified than lay- 

 men might suppose so inconspicuous, unobtrusive a group could 

 awaken. In more than one respect, they form a sharply marked 

 point of departure for the morphological and phylogenetical 

 study of the higher plants. The diversified forms of adaptation 

 which these plants, and particularly the leafy mosses, exhibit in 

 their outer and inner structure, are especially worthy of atten- 

 tion. From the fact that they exemplify so many different incli- 

 nations in respect to their local relations, and because, notwith- 

 standing the variety in their forms, they are of relatively simple 

 organization, the investigator's insight into their adaptive struct- 

 ure is made comparatively easy ; and on more than one occasion 

 their study has greatly aided the understanding of the adaptive 

 phenomena of the more highly developed plants. 



An instructive example of the way in which the observation of 

 one order may be applied to facilitate the study of other orders, is 

 afforded in the water-provision of the leafy mosses. Among the 

 simplest in this category are those genera and species that grow 

 on rocks, roofs, and tree-trunks, and are therefore most directly 

 exposed to the rapid exhaustion of atmospheric precipitations. 

 To these belong many Hypnacem — species of Gymnostomum, Bar- 

 hula, Orthotrichum, etc. No special provisions for taking up water 

 have yet been observed in these species. Their leaves all suck it 

 in when it is abundant and swell out, and then completely dry up 

 again as soon as the air has lost its moisture. It is not the taking 

 in of water that interests us in these mosses, but their complete 

 desiccation, which may occur again and again without harm to the 

 vitality of the plant. In this is expressed a form of adaptation 

 which is invisible to the investigator in microscopic anatomy, and 

 which depends upon undetected properties of the protoplasm. It 

 is evident that this kind of adaptation is most direct and effective, 

 and is in exact conformity with the biological principle of econ- 

 omy of material, in that it makes special protective provisions for 

 the prevention or retardation of the waste of water superfluous. 

 The question arises. Why does this apparently advantageous pro- 



