310 VEGETABLE ORGANOGRAPHY. 



be the formation of a new shoot for the 'stem to elongate 

 again. We can easily perceive these different shoots in 

 the old stems of Polytricha. As to the growth in 

 diameter, it appears to me to take place only at the first 

 period of development : these stems perceptibly retain 

 the same diameter throughout their whole length, and 

 almost at all ages. 



The roots of Mosses are generally fine filaments, of 

 a brown colour, more or less branched, which spring 

 either from the base of the stem, as in Phascum, and 

 which are called Primary Roots, because they are 

 developed at the origin of the plant ; or along the stem, 

 and then they are named Secondary Roots, because 

 they are developed after the first, during the whole life 

 of the plant : they have been seen to issue from the 

 leaves. They are especially frequent in most Mosses 

 which live in turfy ground ; it is not rare to find in the 

 Mosses of these localities, which are perennial, all the 

 lower part of the stem abundantly covered with a brown 

 tissue, formed of an innumerable multitude of roots. 

 But no one, to my knowledge, has yet carefully studied 

 either the structure or mode of absorption of these 

 organs. Mosses which live on rocks seem entirely de- 

 void of them, and, as they can draw nothing from the 

 rock itself, it is likely that their first radicules are intro- 

 duced into the imperceptible fissures, and thus serve to 

 fix the young plant, but that, afterwards, it is nourished 

 by the absorption of its leaves rather than by that of its 

 roots. This mode of absorption, which is found in all 

 Mosses, combined with the dry and half-dead appear- 

 ance which their roots very quickly acquire, causes me 

 to think that these organs do not influence the absorp- 

 tion, except in their infancy, and afterwards remain 

 around the stems of those growing in turfy places, as if 

 to serve for their protection against wet. 



