Cheilanthes and Pellaea . 677 
the interpolation of an extra leaf at a place where primitively two are given 
off, an arrangement still maintained in sections 10-19. 
The detailed anatomy of the stelar tissues furnished results of some 
interest. In none of the five xerophilous Ferns was there to be seen any 
protoxylem, though search was made in both transverse and longitudinal 
sections. In Cheilanthes Fendleri and Pellaea andromedaefolia the apical 
region was thoroughly examined, and it was clear in these cases that there 
was no special protoxylem, the tracheides to be first lignified being large 
scalariform elements scattered irregularly in the xylem. 
There was found to be a close correlation between the stelar structure 
and the amount and arrangement of the wood within the stele. Cheilanthes 
Fendleri and Ch. gracillima , of which the former is perfectly solenostelic 
and the latter scarcely departs from this type, both have xylem forming 
Fig. 7* Cheilanthes Fendleri. Transverse 
section of stele of stem at edge of leaf-gap. 
e.ph. — external phloem ; i.ph. = internal 
phloem. 
Fig. 8 . Portion of transverse section 
of stele of stem of Cheilanthes lanugi- 
nosa. i.ph. = internal phloem ; e.ph. 
= external phloem ; tr. = tracheide ; 
par. = parenchyma. 
a narrow continuous band of tracheides, not broken up by parenchyma 
(Fig. 7). Cheilanthes lanuginosa is intermediate between the simple types 
and the large-stemmed dictyosteles. It has a wider band of wood somewhat 
broken up by parenchyma (Fig. 8). Cheilanthes persiea and Pellaea andro- 
medaefolia are large-stemmed dictyostelic forms with a broad band of wood, 
among which a good deal of parenchyma occurs (Fig. 9). 
The phloem of these forms is remarkable for the absence of differentia- 
tion into protophloem and metaphloem. The total number of sieve-tubes 
is in no case very large. These elements are narrow and arranged in 
a single line on each side of the xylem ring. The whole of the phloem 
in these Ferns may fairly be said to correspond with the protophloem of 
mesophytic species, the slow growth necessitated by a xerophilous habitat 
rendering unnecessary those facilities for active translocation which would 
be given by large metaphloem elements. 
z z 2 
