A natomy of Solenostelic Ferns. 7 1 5 
it flattens out dorsiventrally and finally divides into two by 
constricting in the middle. The constriction usually takes 
place in such a manner that there is no communication between 
the tissues within the xylem-ring and those without it. Some- 
times, however, a leaf-trace is given off at the same time as 
the stem-branches, and then the leaf-gap occurs just between 
the two branch steles and the ground-tissue is decurrent 
through it in the ordinary manner. The sclerenchymatous 
ground-tissue enclosed within the stele is always in direct 
continuity with that decurrent through the leaf-gaps, except 
a few very small strands which occasionally occur in the 
neighbourhood of the branchings. These strands are com- 
pletely surrounded by their own endodermis and appear to 
be quite isolated. The leaf-trace departs as a single strongly 
curved strand, and the curvature increases as it passes out, 
until sometimes the margins of the gutter meet adaxially 
and fuse up so as to enclose a small mass of ground-tissue 
(Fig. ai). This completely closed ring is only to be found 
over a very short distance ; it may never even be formed at 
all. In either case the leaf-trace eventually divides into two 
separate halves. 
Davallia repens. 
The peculiar nature of the vascular system of Davallia 
repens was first observed by Tr^cul 1 in 1885, but in his 
account the most interesting feature of its structure was un- 
fortunately overlooked. However, the same type of stele has 
recently been discovered in certain Lindsayas by Tansley and 
Lulham (l.c.), who have given it a perfectly correct inter- 
pretation. Davallia repens is referred to here because it is 
necessary to complete the series begun by D. aculeata and 
D. pinnata ; for the structure of its stele throughout the whole 
stem is similar to that found in D. pinnata at the base of the 
internodes only. In fact there is no ground-tissue to be found 
1 Observations sur la structure du systeme vasculaire dans le genre Davallia, 
et en particular dans le Davallia repens. Comptes rendus, tom. ci, p. 1453, 
1885. 
