SECT. vin. FERN STEMS. 339 



It is evident that there is an essential difference 

 between the archegonium of the Marchantia, and that 

 of the ferns. The archegonium of the Marchantia 

 merely produces a sporangium, while that of the ferns 

 produces a new plant, and is therefore, in some sense, 

 analogous to the seed of one of the higher vascular 

 plants, though there is no affinity between the two. 



The roots of ferns, like those of forest trees, are delicate 

 fibres, which descend either from a woody stem called a 

 rhizome, from rhiza, a root, or from a caudex, so named 

 from the Latin, caudex, a trunk. Thus the stems of ferns 

 are of two distinct types. The rhizome generally grows 

 horizontally, and creeps along the surface of the soil or 

 rock, or tree trunk to which it is affixed, but it is some- 

 times subterranean. In this, the growing point is in 

 advance of the fronds, which appear at intervals along 

 the exposed side or sides, and after they have reached 

 maturity drop off, leaving a clean scar or cicatrix. The 

 caudex varies from the size of a small wire-like thread 

 to the size of a tree trunk. It is sometimes elon- 

 gated, as in the superfine wiry thread-like stems of 

 Hyinenophyllum, the scandent ivy-like rooting stems 

 of Stenochlsena, and the subterranean, horizontal, 

 widely-creeping stems of Pteris aquilina, all of which 

 develop single fronds at intervals, but fronds which 

 adhere permanently to the stem, and which do not fall 

 off, leaving a scar, as do the fronds borne by the rhizome. 

 The more frequent form of caudex, however, is that of 

 a short stocky stem producing fronds on all sides from 

 its apex: very frequently this is a globose or oblong 

 mass growing erect, yet scarcely reaching above the 

 surface of the soil ; but sometimes it is more lengthened, 

 showing a more or less elevated stem, or turning side- 

 ways, and taking a decumbent position, the young fronds, 

 however, always rising from its apex. It is on the latter 

 plan, by a continuous erect and upward growth, that the 



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