21 



few fragments of woody fibre. My examinations of these curi- 

 ous mosses have proved that in moist climates, on the banks of 

 rivers, or on mountains covered with clouds, their existence and 

 their growth is by no means necessarily dependent upon the soil 

 which they cover. For these mosses, by their peculiar conforma- 

 tion, are so exceedingly hygroscopic that they imbibe moisture 

 in all parts of their tissue, both from the base upwards, and by 

 their leaves, stalks, &c. This peculiarity is not due, as some 

 have supposed, to a mechanical capillarity, but to the nature of 

 their tissue, to the disposition of their fibres, and to the entire 

 absence of chlorophyl, wherein these plants resemble the most 

 simple substances. For vegetable tissue, as you know, is hygro- 

 scopic in proportion to its freedom from particles of a foreign 

 nature. I shall give a more satisfactory exposition of this matter 

 in a special work ; but you have often observed, without doubt, 

 the curious hygroscopic power of Sphagnum. For if you pull 

 ofi^a tuft, even from the driest part of a swamp, on pressing it 

 between your fingers you will always find water running from it 

 as from a sponge. These plants imbibe moisture in this way from 

 the atmosphere, if they cannot obtain it from the soil. Thus, a 

 tuft of Sphagnum, weighing in a completely dry state, three 

 pennyweights twelve grains, suspended in the air during a 

 foggy night, absorbed seven grains of water. On the other hand, 

 evaporation by the tissue is excessively slow, and out of propor- 

 tion to the absorption. 



Another tuft of Sphagnum, about twenty-two inches in su- 

 perficial extent, and four and a half inches high, and weighing 

 when dried one ounce twenty-one pennyweights, was put into a 

 vase having at the bottom a hole of half an inch diameter. 

 Through this hole, and touching the water with one fourth of a 

 line of the ends of its stalks, the tuft became completely satur- 

 ated in less than two hours, having absorbed a pound of water. 

 The same tuft, being then exposed to the air and sun for thirty- 

 six hours, lost only five ounces by evaporation. Upon the 

 basis of these facts you may easily follow the operations of 

 nature in the formation of Cedar Suamps. 



A little water remaining in a hollow, and saturated with humic 

 acid by the decomposition of vegetable substances. Sphagnum 

 immediately establishes itself. You know how it grows, in com- 



