EXTERNAL APPEARANCE. 19 



Inform the stems are mostly rouudecl, though they vary 

 in different genera, and this diversity depends in a great 

 measure on the form and consistence of the leaves, which 

 are often closely adpressed to, or arranged in particular 

 order round, the stem. 



The terms used in describing the stems and foliage of 

 higher plants, are equally applicable to those of Mosses, 

 and therefore some previous acquaintance with a Botanical 

 Glossary is a usefid preliminary to their study. 



We now proceed to say a few words on the Foliage of 

 Mosses. Though the Biurhanmia apliylla, or leafless Bux- 

 baumia, from its specific name may seem to be an exception, 

 there are no true Mosses without distinct leaves, for even in 

 this curious plant Brown discovered, at the base of the foot- 

 stalk, minute leaves, seemingly composed of fine shreds. 

 As in higher plants we have different classes of leaves, so 

 here we find a variety according to the station they occupy 

 on the plant : these are known to Muscologists as cauline 

 and perichsetial, or those clothing the stem and those im- 

 mediately surrounding the base of the fruit-stalk or seed- 

 vessel. 



They differ however in some very important particulars 

 from the leaves of other vegetable tribes, and it may be well 



