Anatomy of So lenost die Ferns : /. Loxsoma . 79 
from each other are reduced to such an extent that they form 
a coarse network only, the meshes of which are occupied by 
the sieve-plates themselves. Those elements of the phloem 
furthest away from the xylem on either side of the solenostele 
are very narrow, angular and flattened, with thick and glistening 
walls ; in older regions almost disorganized. They constitute 
the protophloem, which is very clearly to be distinguished on 
either side of the solenostele. The central portion of the 
stelic ring is occupied by the xylem, which consists of scalari- 
form tracheides with a few cells of intervening parenchyma ; 
a layer of the latter also surrounds the xylem-strand, separating 
it from the phloem on both sides. The tracheides of the 
xylem increase in size from without towards the centre of the 
rhizome (Fig. 2), the smallest elements being on the outside. 
In sections near the apex, where the xylem is not yet fully 
developed, it may be seen that the smallest tracheides at the 
external periphery of the strand are the first to be differentiated 
(Fig. $,prx\ and it is especially to be observed that they are 
not collected into definite localized groups, but are fairly 
evenly distributed all round the external periphery. These 
first-formed elements are all scalariform tracheides ; even 
after most careful research I have failed to discover any 
annular, reticulate, or spiral elements whatever in the stem, 
except on the upper surface just at the point of insertion of 
a leaf-trace, and these clearly are to be considered in relation 
to the latter. It is true that these first-formed elements of 
the xylem differ from typical protoxylem both in distribution 
and structure, and that they are only to be distinguished from 
the rest of the strand by their smaller size and early develop- 
ment, yet I think it is permissible to state that the protoxylem 
proper to the stem in Loxsoma consists of narrow scalariform 
tracheides evenly distributed around the external periphery of 
the xylem-ring. The walls of the scalariform tracheides of 
Loxsoma , in common with those of other Ferns and also of 
Mar site a 1 , when treated with caustic potash or any other 
macerating reagent, partially dissolve, in such a manner as to 
1 Cf. Russow, Vergl. Untersuch. , loc. cit. 
