276 LETTER XXIV. 



ner far more complete than Ferns, or Club-mosses, 

 althoufT^h thev are destitute of air vessels and breath- 

 ing pores. Mosses are usually the first plants that 

 shew themselves on rocks, or walls, or barren places, 

 where no other vegetation can establish itself; pro- 

 vided the air is damp they will flourish there, and in 

 time, lay the foundation of a bed of vegetable mould, 

 in which the roots of grasses, and other stronger 

 plants may find support, till they, in their turn, have 

 decayed and prepared the way for shrubs and trees. 

 This is the usual order observed by nature in con- 

 verting the face of rocks into vegetable mould, and 

 thus you see Mosses have to perform the office of 

 pioneers to larger plants, an office for which one 

 would have thought their Lilliputian size would 

 hardly have qualified them. 



Mosses are formed upon precisely the same plan 

 as flowering plants, as far as the arrangement of their 

 organs of vegetation. They have, in all cases, a 

 stem, or axis, however minute, round which the 

 leaves are disposed \\Tth the greatest symmetry — 

 (Plate XXIV. l.fig. 2.); they have the jjarts that 

 answer to seeds, enclosed in a case, and this case is 

 elevated on a stalk, which arises from among the 

 leaves. But, beyond this, analogy ceases ; in all 

 other points of structure, the Moss tribe is of a most 

 singular nature. 



Mosses are said to be in fruit when the stems are 

 furnished with brown hollow cases, seated on a long 

 stalk {fig. 1. 2.). It is chiefly of this fruit, or theca, 

 or sporangium, and its modifications, that we make use 



