44 Lang. — Prothalli of Ophioglossum pendulum 
for the greater part of its course through the cortex somewhat 
different (Fig. 68). The difference consisted in the presence 
on the adaxial face of the bundle, separated from the proto- 
xylem by some parenchymatous cells, of a few larger 
tracheides ; the trace was thus mesarch. This agrees with 
what is found in the mature plant and suggests that the stele 
was in these cases probably mesarch also. The trace passes 
obliquely through the cortex, and may either enter the leaf- 
stalk as a single bundle or before doing so have divided into 
two bundles which face inwards and slightly towards one 
another (Fig. 69). No further divisions occur in the petiole 1 . 
In most cases, even in relation to the first leaf, the slit-like 
organ, described for the older rhizome by Mr. Gwynne- 
Vaughan in the present number of this Journal, could be 
traced down to the stele in front of the leaf. In the examples 
it was possible to study fully a similar disturbance of the 
endodermis to that described for the older plant was found in 
relation to this organ where it approaches the stele. 
It is unfortunate that a complete series of stages between 
the solid monostele of the young plant and the stele of the 
mature plant with an internal endodermis was not available. 
The facts mentioned in the above description with regard to 
the variations in the size of the pith in the seedlings suggest 
that the transition is a gradual one, taking place by the 
increase in size of the pith, its limitation from the xylem by 
an indefinite endodermis and the appearance of definite leaf- 
gaps. The study of the young plant thus supports the view, 
expressed by Farmer and Freeman, that the occurrence of the 
internal endodermis in this plant is secondary and is connected 
with the appearance of leaf-gaps. 
Summary. 
Ophioglossum pendulum. 
1. The prothallus is a colourless saprophyte; it is usually 
branched, the short branches radiating in all directions into 
1 Sometimes an intercellular space arises by the breaking down of cells on the 
adaxial face of the bundles in the leaf-stalk, but this is not a constant feature. 
