INTRODUCTION. xvii 



roots striking into the adjoining stems. Nay, such is the dis- 

 position manifested by some Mosses to throw out roots, that not 

 a few of them are known to produce them at the extremity of 

 their leaves ; as does Hookeria lucens. 



Very rarely are the stems wanting in the order Musci. Some 

 individuals of the genus Phascum have very short ones, as have 

 Buxbaumia aphylla and Diphyscium foliosum. Those stems that 

 grow upright are usually but little branched ; those that creep 

 upon the ground are very much so. 



No species of Moss is altogether destitute of foliage, although 

 Buxbaumia aphylla, as its name implies, was long supposed to be 

 without any. But the acute Mr. Brown has detected leaves of a 

 very minute size, and cleft in a palmated, or almost digitated, 

 manner ; which is the more remarkable, because there is not known 

 another instance, throughout the whole order of Musci, in which the 

 leaves are, in the slightest degree, divided, farther than just at 

 their margins into minute teeth or serratures. Nor is there ever 

 found among the Mosses, a petiolated leaf, or one placed 

 upon a footstalk. But the leaves themselves vary most strikingly 

 in form and outline in different species, and furnish specific 

 characters of great importance. Nor does any Moss exist 

 having hairy foliage, all are glabrous. Some, indeed, as Neckera 

 trichomitryon and Neckera hirtella, Weissia ciliata, &c. have mar- 

 ginal ciliated processes ; but they are never on the superficies of 

 the leaf. Some are nerveless, but the greater number have a 

 strong nerve, running through the whole centre of the leaf, from 

 the base to the summit ; others have two nerves, which are paral- 

 lel to one another, and pass on each side of the centre of the leaf: 

 and these nerves are only formed of closely compact cellules. 



In general, the Mosses may rank among the smallest of vege- 

 tables ; we know of some that are scarcely visible to the naked 

 eye ; but which yet are as curious and complicated in their struc- 

 ture as the larger kinds ; a few of which attain, if they do not 



b 



