226 IMPERFECT PLANTS. 



with Moss can be removed to a distance with greater 

 safety than when protected in any other way, and ac- 

 cording to the observations of Gleditsch, they grow with 

 as much luxuriance when nourished merely by Moss 

 as when in the most fertile soil. Some Mosses thrive 

 only in marshy situations which they annually enrich 

 by the deposition of new mould. The Hercynian for- 

 est, once an impenetrable morass, has through the 

 agency of the Grey Moss Sphagnum palustris, been con- 

 verted into a fertile soil, and the yellow corn now 

 waves over the fields which have been forming for 

 ages. Thus we owe to insignificant mosses the largest 

 rivers, the draining of extensive marshes, and the fertil 

 ityof some barren fields.* 



3. HEPATIC^. 



These are small herbaceous plants whose herbage 

 constitutes a frond, and whose fruit like that of the 

 Mosses is enclosed in a capsule. The veil, however, 

 by which this capsule is sometimes enclosed, usually 

 opens at the summit, nor is it furnished with a lid, 

 analagous to the one we have seen in the fructification 

 of Mosses. This is a small and by no means interest- 

 ing tribe of plants. The student who wishes to gain 

 an idea of their singular structure, will find the com- 

 mon Brook Liverwort, Marchantia polymorpha an ex- 

 ample well calculated to exhibit the frond, but the 

 peltate receptacle on which its fructification is borne is 

 very different from the capsules of the other genera. 

 In Jung ermannia, Fig. 119, the capsule is four-valved, 

 and when the seeds are mature, these valves separate 



* Willdenow. 



