THE HIGHER CRYPTOGAMIA. 251 



heart-shaped. The cells of the place of attachment, and 

 often also those near it, divide, when the frond is almost 

 perfect, by means of septa parallel to the surface of the 

 frond (PL XXXIV, fig. 7). The cells of the lateral margins 

 of the leaf often grow into delicate little teeth, which are 

 usually curved backwards. 



Scales which run through all the stages of development 

 here represented are found not only on the principal axis 

 of the plant but also on the lower portion of the frond. In 

 the greater number of ferns the bases of the fronds exhibit 

 scales at least in their youth. The arrangement of the 

 scales both on the principal axes and on the fronds is 

 governed by well-defined rules.* The reason why the 

 arrangement is often undistinguishable on the fronds is 

 that after the last important longitudinal expansion of the 

 stipes individual scales fall off abnormally much earlier than 

 the neighbouring ones. 



In the earliest stages of Polypodium vulgare scales are 

 found whose almost circular form indicates the tendency to 

 assume the shape of a shield which is ultimately arrived at 

 by the exuberant growth of the hinder margin, in which 

 growth those daughter-cells take part which are derived 

 from the primary cell, which after numerous divisions by 

 means of longitudinal septa has become the attachment-cell 

 (PL XXXIV, fig. 7). 



The separation of the vascular bundles from the rest of 

 the tissue of the stem, and the formation of roots from 

 them, take place as in Aspidium and Pteris. In Poly- 

 podium vulgare, as in Polypodium aureum, the vascular bun- 

 dles run off into a cylindrical annular net of meshes, which 

 have no immediate relation to the insertions of the fronds, f 



Platycerium Alcicorne. — The first frond of the germ- 

 plant is erect and fleshy, having the shape of a spatula, 

 and being slightly bent over behind. It is clothed with 

 the stellate hairs characteristic of the plant, and has but 

 few scales. The latter are more abundant on the young 



* For instance, on the principal axis and fronds of Niphobolus chinensis the 

 arrangement is f s . The regularity of the arrangement is beautifully shown on 

 the procumbent stem of Polypodium aureum by the little depressions, of which 

 each one indicates the place where a scale has been attached. 



f See V. Mohl, 'Vermischte Schriften,' p. 115. 



