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Boodle . — Anatomy of the Gleicheniaceae . 721 
upwards to while the lower one has divided into b 1 , and b 2 ., 
and A has divided into a., a . The lower a. and also b 2 . will 
remain in the stele, while the upper a., b. and b 1 . will pass out 
as the three protoxylems of the leaf-trace. In the stage we 
are considering (Fig. 17) the nodal island (n.i.) has increased 
greatly in size, and other tissues besides parenchyma have 
become differentiated in it. There is a central mass of brown 
sclerotic tissue (sc.) surrounded by an endodermis, and on the 
lower side of the island are a few sieve-tubes, represented by 
short lines in the diagram. Detailed drawings of a similar 
nodal island are given by Poirault (’ 93 , p. 175, Fig. 15) for 
G. pubescens, H. B. K., var. (under the syn. G . furcatd). As 
described by Poirault, the first appearance of the sclerotic 
group, as one goes towards the node, is one fibre sheathed by 
endodermis ; then more and more fibres are added until the 
group, still surrounded by an endodermis, attains considerable 
size. Passing on from Fig. 17, the thickness of the parenchyma 
increases on the inner side of the sclerotic group, the phloem 
in the nodal island increases in amount, and splits into two 
bands, which become separated by a bar or bridge of xylem 
appearing between them, as seen in Fig. 18, PI. XXXIX. I11 
the next stage (Fig. 19), the xylem of the leaf-trace has 
become separated from that of the stele by the splitting of 
this bar of xylem. Consequently part of the original nodal 
island passes off inside the leaf-trace, and contains the sclerotic 
tissue and a band of phloem ; while part of the nodal island 
remains enclosed in the xylem of the stele (n.i.). It still 
contains a few sieve-tubes, but these soon disappear, and the 
parenchymatous island shrinks in size, until it is reduced to 
a few cells accompanying the protoxylem b 2 . in the internode. 
A new upper median protoxylem is supplied by the division 
of a., and the typical internodal structure is restored. 
In a second node of G. dichotoma , the xylem of the leaf- 
trace again passes off closed ; the only difference of detail 
is that, in the stage a little later than Fig. 17, three or four 
sclerotic elements, apparently surrounded by an endodermis, 
branch away from the main mass at the same time that the 
