480 Boodle .— Anatomy of the Hymenophyllaceae. 
collateral structure in the rhizome, viz. T. muscoides, Swartz, 
and T. membranaceum, Linn. 1 The xylem consists of a small 
group of tracheides (6-8), of which the small ones representing 
protoxylem lie towards the lower side ; the phloem occurs 
on the upper side of the stele only. Fig. 41 is a transverse 
section of the rhizome of T. muscoides. This structure, though 
very much more delicate, resembles the monarch stele of the 
root of Ophioglossum vulgatum ; a corresponding structure 
thus appears to have been produced by reduction from two 
entirely different structures, namely from a xylem-ring with 
central protoxylem, and surrounded by phloem in the one 
case, and a typical diarch root-structure in the other case. 
A case of greatly reduced structure is described by Giesen- 
hagen 2 in the rhizome of a species of Trichomanes described 
as T. microphyllum , Ghgn., but in a later paper 3 united with 
T. labiatum, Jenman. In this species the endodermis surrounds 
a bundle consisting of nothing but one tracheide surrounded 
by four to five parenchymatous cells. A still further reduc¬ 
tion is found in T. Motleyi , described by Karsten 4 ; in this plant 
the stem possesses no tracheides, but only a few conjunctive 
parenchyma-cells. The sterile leaf has no tracheides, but the 
fertile leaf has a true vascular bundle. 
In T. muscoides the petiolar bundle is practically identical in 
structure with the stele of the rhizome, both being collateral 
and of about the same size. In the species with sub-collateral 
structure in the rhizome, the petiolar structure differs only in 
the interruption of the phloem ; being collateral. 
The above description of different species of the genus 
Trichomajies shows a considerable range of structure in the 
stele ; the chief types being :— 
1. A ring of xylem surrounding a fair-sized mass of paren¬ 
chyma, which contains the protoxylem. T . reniforme. 
1 Prantl describes collateral structure of the rhizome in his section Hemipklebium 
of the genus Trichomanes ( 1 . c., p. 26). 
2 Giesenhagen, Flora, 1890, p. 445. 
3 Giesenhagen, Flora, 1892, Erganzungsband, p. 178. 
4 Karsten, Epiphytenformen d. Molukken, Ann. Jard. Bbt. Buitenzorg, XII, 
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