192 MORPHOLOGY. 



cells. In Lycopodium inundatum the inner cells exhibit thick annular 

 fibres, similar to what we find in the fruit of the Liverworts. 



The epidermis of the upper and lower surface of the leaves in L. 

 stoloniferum differs very much. The cells of the upper one are thicker 

 walled, and have lying upon them, here and there, long cells, which are 

 beset on the outer side with from two to three rows of warts. The cells 

 of the under surface are thinner walled, and contain chlorophyll ; while 

 between the two a somewhat spongy cellular tissue is interposed. The 

 stomata are only found upon, and close to, the leaf-rib of the Lycopodia. 

 The annular fibres in the capsule-wall of L. inundatum were first 

 observed by Bischoff *, who, however, gives an incorrect and very far- 

 fetched explanation of them,, that might be at once refuted by a consider- 

 ation of their early condition. 



VII. FERNS (FILICES). 



107. In the germination of the Ferns the spore-cell breaks 

 through the external membrane and expands, in some even at an 

 absolutely definite, previously indicated point, into a longer or 

 shorter tube, whose extremity forms new cells, which gradually 

 arrange themselves into a flat, generally bilobed, proembryo ; a few 

 of these cells expand downward into adhering fibres. At a definite 

 part of this proembryo there is formed a group composed of thicker 

 cellular tissue, and, by degrees, a small ovate corpuscle, one ex- 

 tremity of which is prolonged into a root, and the other into a bud, 

 forming the stem and leaf. 



The stem then assumes two essentially different modifications, in 

 one of which it does not expand, and in the other of which it docs 

 so to a great length between every two succeeding leaves (which are 

 always closer together at their first origin than they appear subse- 

 quently). In the first case the stem mostly creeps subterraneously, 

 so that the leaves alone appear above the ground, as in Pteris 

 aquilina, or it creeps upon the ground or up trees and rocks (as in 

 Lomaria scandens) ; in the second modification it again exhibits two 

 further differences, according as the root, and subsequently the 

 stem, constantly does or does not die off from below. In the former 

 case it rises but inconsiderably above the earth, occasionally lying 

 obliquely in it (as in Aspidium Filix mas) ; in the latter case it grows 

 (but only under the tropics) into a considerable sized trunk, some 

 twenty or thirty feet in height (tree-fern, as, for instance, Cyathea, 

 Dicksonia, Alsophila., &c.). Almost all stems exhibit adventitious 

 roots (radix adventitia\ arising in a peculiar mariner from the stem, 

 and occasionally investing the trunk with a thick network (as 

 Cyathea Schansin). 



The leaves of Ferns are mostly stalked, seldom sessile, generally 

 divided into lobes at the margin (occasionally in the most various 



* Die kryptogamischen Gewiichse, p. 109. 



