730 Boodle. — Anatomy of the Gleicheniaceae. 
of other Mertensias , e. g. the form of G. longissima described 
above, though smaller than in the latter. 
To return to Fig. 26 for some details connected with the 
separation of the leaf-trace, there is a protoxylem-group 
in the xylem just below the tip of each arm of the scleren- 
chyma. Phloem is of course found surrounding the whole of 
the xylem, and, on the inner side of the latter, it is found 
as a continuous layer, interrupted only below the middle 
region of the arch of xylem destined for the leaf-trace. Of 
the phloem-elements present within the lower parts of the 
xylem-arch a few are transformed into fibres, and the latter 
are also found in the phloem between the tip of each arm 
of the sclerenchyma and the adjacent protoxylem-group, 
already mentioned. This protoxylem forks into two, of which 
one group goes to supply the future hook of the leaf-trace, 
while the other one remains in the stele, still with the phloem 
containing fibres between it and the sclerenchyma. Then 
a bar of xylem is formed cutting across the arm of scleren- 
chyma near its tip ; the latter having become previously 
elongated as on the right-hand side in Fig. 26. In this way 
a piece of brown sclerotic tissue (apparently surrounded 
by an endodermis) comes to be enclosed in an island 
in the xylem, in which also phloem is found, though chiefly 
represented by pale-walled fibrous elements, and this island 
is adjacent to a protoxylem-group. Next the bar of xylem 
splits, so that the xylem of the leaf-trace is separate from 
that of the stele, then phloem, endodermis, &c., appear in the 
gap so that the end of the leaf-trace becomes free from 
the end of the solenostele. The above stages do not take 
place simultaneously at the two ends of the leaf-trace, as it 
swings round slightly so as to pass off obliquely. In Fig. 27 
two dark patches are seen immersed in the xylem of the 
open solenostele near its two ends. These are the two islands, 
whose formation has just been explained. They contain 
brown sclerenchyma, parenchyma, and phloem-fibres. The 
brown fibres in the two islands are not continued above 
the node for any great distance after the separation of the 
