Anatomy of Solenostelic Ferns . 719 
that of Cheilanthes lendigera (cf. p. 696). At the level of the 
leaf-gap the internal ground-tissue is fairly voluminous, but 
it rapidly decreases as it passes down the internode until only 
a small strand is left lying close to the dorsal side of the 
stele. In my specimens this also eventually disappears, so 
that the decurrent ground-tissue is not continuous from one 
leaf-gap to another. The stele, therefore, in its general 
appearance resembles that of Davallia pinnata , but on closer 
comparison some very important differences come to light. 
In the first place the xylem-ring of Vittaria stipitata is 
equally narrow on all sides of the stele, and secondly, as the 
internal ground-tissue disappears it is not replaced by phloem 
but by pericycle. Only a slight amount of internal phloem is 
present at the most ; it is even completely wanting on the 
ventral side of the stele, being replaced by parenchyma. 
A number of plants identified as Vittaria elongata were 
also investigated, and in some of them the stele possessed 
exactly the same structure as in V. stipitata. In others the 
ground-tissue did not pass in through the leaf-gaps at all, 
so that, apart from the thin internal sheath of phloem, the 
whole of the centre of the stele was occupied by pericyclic 
parenchyma, even at the level of the leaf-gap itself. In 
several other specimens, again, the vascular system proved 
to be distinctly dictyostelic and of the simple dorsiventral 
type described on p. 695. According to Poirault 1 no internal 
phloem whatever is to be found in this species, and Jeffrey 2 
states that both the internal phloem and the internal endo- 
dermis are wanting, but a certain amount of internal phloem 
was present in all the specimens that I examined, although it 
is replaced by parenchyma on the ventral side. It is rather 
surprising to find so wide a variation in the vascular anatomy 
of one and the same species, and since it is very difficult to be 
quite sure about the identification of some of the Vittarias 
1 Recherches anatomiques sur les cryptogames vasculaires, Ann. des Sc. Nat., 
7 e s<Sr., t. xviii, p. 179, 1895. 
2 The structure and development of the stem in the Pteridophyta and Gymno- 
sperms, Phil. Trans. Roy. Soc. Lond., Series B, vol. cxlv, p. 132, 1902. 
