i6q 
Notes . 
corner of the stele, and becomes the meristele of the petiole, its plane 
of symmetry being now parallel with the dorsal surface of the stele. 
The broken dorsal vault becomes again complete before the meristele 
is quite detached (Fig. 12), but in such a way that a bay of the internal 
phloem is left, in the same position as the one below the node. This 
superior bay gradually dies out, and the stele returns to its internodal 
condition. 
The first point of interest about this type of stele is its correspon- 
dence with the condition found by Leclerc du Sablon 1 in the young 
stems of Pteris aquilina (Fig. 15) and Nephrodium molle , and the 
similar condition found .by Mr. Boodle in Anemia Phyllitidis 
(Anatomy of Schizaeaceae, pp. 389-390, and Fig. 26, Ann. of Bot., 
XV, 1901). In these Ferns the central part of the protostele of the 
first-formed portion of the stem consists of a solid cylinder of xylem 
as far as the exit of the first leaf-trace. Close above this point there 
arise in its centre a few sieve-tubes. The appearance of this strand of 
phloem in the midst of the xylem gives to the stele the same essential 
character as that of the internodes of the adult rhizome of Lindsaya 
(Fig. 14). At the departure of some later leaf-trace, the hollow 
cylinder of xylem (together with the mantle of external phloem, 
pericycle, and endodermis) is broken, and the endodermis dips down 
into the centre of the now horseshoe-shaped stele. By the closing up 
of the gap formed by the departure of the leaf-trace, and the inclusion 
within the stele of a strand of parenchyma surrounded by a layer of 
endodermis, the solenostelic structure is obtained (Fig. 18). Higher 
up still the solenostele breaks into two stelar arcs. 
By the writings of Mr. Gwynne-Vaughan 2 and of Dr. Jeffrey 3 we 
have recently been made familiar with the idea that solenostelic 
and siphonostelic structure may be phylogenetically intermediate 
between protostelic on the one hand, and dialystelic or astelic 
on the pther. The solenostelic structure in the young stem of 
Pteris aquilina is ontogenetically transitional between the pro- 
tostelic structure of the base of the first-formed stem, and the 
dialystelic (‘polystelic ’) structure of the rhizome; and so in the 
1 Recherches anatomiques sur la formation de la tige des Fougeres. Ann. Sci. 
Nat., Bot., 1890. 
2 Polystely in the genus Primula , Ann. of Bot. xi, 1897. Studies in the 
Anatomy of the Solenostelic Ferns. I. Loxsoma. Ann. of Bot. xv, 1901. 
a The Morphology of the Central Cylinder in the Angiosperms. Trans. Canad. 
Inst., 1900. 
