Cheilanthes and Pellaea . 
673 
ment of a palisade, and the localization of the stomata on the lower surface, 
where they are protected by the inrolled margins alone (P. andromedae- 
folia :), or by inrolled margins plus a covering of scales (CJi. Fendleri) or 
hairs (the other Cheilanthes species). These characters are shown in the 
figures of transverse sections of leaves (Figs. 1, 2). The most strongly 
marked xerophily is shown in the Pellaea , which possesses a very thick 
cuticle on its upper surface, and has also a palisade, which in the middle of 
the leaf is three cells deep. The lacunar tissue is reduced, and the margins 
are much inrolled. 
Stem Anatomy. 
The stelar anatomy of Cheilanthes and Pellaea is of interest in that 
each genus contains both solenostelic and dictyostelic forms, together with 
others that are intermediate between these types. The four species of 
Cheilanthes investigated are placed next one another in the ‘ Synopsis 
Filicum ’. They are all in § Physapteris , and Hooker and Baker, 
from a study of their external morphology, must have considered them 
nearly related one to another. The stelar anatomy, however, is different 
in each species. In the investigation of this feature series of hand sections 
were cut, and in all except Cheilanthes Fendleri these were drawn, forming 
Figs. 3-6. 
In Ch. Fendleri we have a true solenostele. The leaf-gaps are long but 
fail to overlap. 
In Ch. gracillima (Fig. 3) the stele over the main portion of its course 
behaves as a simple solenostele. At certain points, apparently not in 
accordance with any phyllotactic rule, extra leaves are inserted in such 
a way that two leaves are given off almost exactly together. The result is 
that the two leaf-gaps are at the same level, the stele therefore at such 
points being dictyostelic. Such pairs of leaves are seen in sections 8-10 
and 15-16 in the diagram, Fig. 3. In section 15 there is also a 1 perfora- 
tion ’ or gap not formed by the giving off of a leaf-trace. Most of the leaves 
are given off dorsally, but in sections 8, 25, and 32 this rule is seen not 
to apply. 
In Cheilanthes lanuginosa (Fig. 4) the departure from solenostely is 
still greater, though at intervals the transverse section may be a complete 
ring (sections 15, 16). The leaf-traces may be given off singly (sections 4, 
7, 21), in pairs (section 10), or even in threes (section 17), and the leaf-gaps 
of one series may remain open till the departure of the next series (section 5). 
The stem, as in the two species preceding, is distinctly dorsiventral, a definite 
cauline ventral portion of the stele persisting throughout the stem. 
In Cheilanthes persica (Fig. 5), however, the arrangement of the leaves 
on the stem is radial. The leaf-gaps are also very long, so that this is the 
most pronouncedly dictyostelic form investigated. 
