86 Sykes . — The Anatomy and Morphology of Tmesipteris. 
VII. Summary. 
In conclusion it may be well to give a short summary of the principal 
facts demonstrated in the course of the above research. 
An endodermis has been shown to be present in the rhizome surround- 
ing the single stele and has characteristic markings on its radial walls. 
At the transition region the endodermis does not alter its position, but it 
becomes less and less obvious and loses these characteristic markings ; in 
the aerial stem it can no longer be distinguished as a definite layer. If we 
are to look upon the endodermis as of morphological significance, being the 
layer separating cortex from stele, it becomes impossible to consider the pith, 
which arises in the centre of the stele in the transition region and quickly 
expands to form a large tissue in the stem, of other than stelar origin. 
While in no way wishing to lay stress on such a view of the endodermis, 
it is interesting to note that here we have a protostele passing into a medul- 
lated monostele without the intermediate stage of solenostele, and this 
medullated monostele is already present at a level at which no leaves have 
yet arisen. 
The statements of other authors concerning the growth of the plant 
from a single apical cell have been confirmed, both in the rhizome and 
stem apex. 
The absence of sterile branches is a curious feature in the plants 
supplied to me. It must be sufficient to notice here that the course of the 
vascular bundles in a sterile branch is described by Bertrand, and is exactly 
similar to that found in a fertile branch ; the single bundle entering the 
axis branches into three, the two lateral traces supplying the leaves, and 
the central one presumably representing the vascular supply of the apex. 
In the fertile branches the central of the three bundles supplies the 
synangium which occurs at the point of divergence of the two leaves. 
A single trace thus enters the synangium pedicel and then branches again 
into three, the central one soon terminating, while the two lateral ones 
diverge, and run round the periphery of the septum. The central trace, 
described now for the first time, seems an important piece of evidence in 
favour of the axial theory of the sporophyll in the Psilotales, and is here 
regarded as representing the vascular supply of the apex of the branch. 
This theory appears to me to be also supported by the abnormalities 
described both by Professor Thomas and in this paper. It is concluded 
that the fertile branch in Tmesipteris is of cauline nature, and consists of 
an axis, bearing two leaves or a single dichotomously branched leaf (which 
have possibly only become associated with it in the course of evolution), 
and terminating just above their origin. At its apex is borne a synangium 
which is formed from one or two masses of sporogenous tissue, which have 
fused over the apex of the branch. 
