220 DIPTEROID FERNS [CH. 



The dermal scales repay attention. They are peltate, and are borne on 

 emergences, so that they project slightly from the surface. The cells forming 

 the single layer have thickened dark-brown walls, except near to the attach- 

 ment, and at the extreme margin : they are, in fact, of the clathrate type, and 

 resemble those of Christopteris triciispis (Fig. 728, a, b): but in this Fern 

 there are marginal glands. Christ describes the margin in NeocJieiropteris as 

 ciliate: but old scales do not show this, possibly owing to shrivelling with 

 age ; for occasional appearances suggest collapsed glands. On the other hand, 

 in C. triaispis they are not constant. Such glands are present in Platycerium, 

 and in some Polypodioid Ferns (Fig. 728, c, d). 



Anatomically this Fern is in advance either of Ulatonia or Dipteris. The 

 rhizome contains a highly perforated and disintegrated stele, represented in 

 transverse section by a circle of about a dozen small meristeles: of these 

 about five constitute the highly disintegrated leaf-trace, which passes off 



Fig. 728. Margins of scales of various Ferns, showing structure and marginal hairs. rt= Christopteris 

 triciispis. b — Neocheiroptcris. c= Platyceriuiii a^. d=GoniophU'l>iii»i %]i. (X85.) 



obliquely upwards. In fact the vascular system closely resembles that of 

 Christopteris, or oi PJiyiiiatodes. There are also numerous sclerotic nests, es- 

 pecially towards the upper side of the rhizome. 



The relation of the sori to the venation of the blade presents points of 

 interest. The basal region of a leaf is shown in Fig. 729. The sori lie close 

 on either side of the main veins, but only on the acroscopic side of those 

 forming the helicoid curve: they vary greatly in size, and are specially 

 elongated at the base of the blade. They have never been seen seated on a 

 vein-ending, but always on a continuous vein, or on a plexus of veins: in 

 fact, their relation is variable. Frequently a large vascular loop underlies a 

 large sorus, but a small one may be seated on a single vein which still con- 

 tinues its course (Fig. 730). These facts point to a spread of the sorus over 

 an enlarging area. It will be seen later that the vascular elaborations beneath 

 the sorus find their parallel in some related "Polypodioid" types (p. 225). 



