Anatomy of Solenostelic Ferns . 693 
lateral shoots are borne by any of the above Ferns they are 
always inserted upon the base of the petiole, and their 
vascular systems are joined on to one or the other margin of 
vascular strand of the petiole (cf. Figs. 4, 5, and 6). 
A perfect solenostele is also present in the stem of Hypolepis 
tenuifolia, millefolium , distans, and repens , but certain additional 
peculiarities occur in relation to the insertion of the leaf- 
trace which will require especial description. The stem is 
a dorsiventral rhizome, as in the Ferns mentioned above, with 
the leaves arranged in two rows upon the upper surface. 
The leaf-trace becomes definitely marked off from the rest 
of the solenostele some distance before it actually departs as 
such, and the gap formed by its departure runs forward a 
considerable distance before it is closed up again. The leaf- 
trace consists of a single curved strand in all cases except 
in H. tenuifolia , where it departs as two separate pieces, and 
later on in the petiole breaks up into several. One or 
more lateral shoots are given off from the base of each leaf 
in all four species. If only one is present it always arises 
from the basiscopic margin of the leaf-trace, if there are two 
or more, then the lowest on the basiscopic side is always 
stronger and further developed than the others (Fig. 6). In 
order to form the vascular system of a lateral shoot the margin 
of the leaf-trace curls inwards on to itself, and the curved 
portion eventually separates off as a gutter-shaped stele which 
rapidly closes up into a complete cylinder. 
Reference to Figs. 4, 5, and 6 will show how this takes place, 
and also how the presence of the lateral shoots affects the 
form of the leaf-trace and the manner of its departure: At 
the very base the leaf-trace is very irregular in form, and its 
concavity is directed towards the apex of the stem, but once 
it has become free from the steles of the lateral shoots it 
exhibits the customary form of an arch, the concavity of 
which faces the median dorsiventral plane of the rhizome. 
The structure of the node in these Ferns is still further 
complicated by the appearance of certain small vascular 
strands which connect up the free margins of the leaf-trace, 
