206 
Lang —Studies in the Morphology and 
directed attention to the problem of the medullation of the Ophioglossaceae. 
The facts to be described are in substantial agreement with his results, but 
they go beyond them and have led to somewhat different conclusions. 
Before describing the six plants in order the relations of the endodermis 
to a departing leaf-trace as seen in transverse sections may be referred to. 
The ordinary type in the adult region is represented in Text-fig. i ,a-d. 
The earlier preparations for the departure of this trace are seen in Text - 
fig. 9. 20, 21 ; this shows how the xylem separates first on one side, and that 
Text-fig. i. Endodermal relations in the departure of a leaf-trace from the adult 
region of the stele. Description in text. 
a bulge in the endodermis indicates the commencing departure of the trace. 
This arc of endodermis accompanies the trace on its abaxial side (Text- 
fig. 1, a b , c). On the separation of the trace an open gap is left in the 
endodermis of the stele (Text-fig. 1, c), but the endodermis continues 
inwards on either side for a short distance round the margins of the gap in 
the xylem. The interest of this particular node is 
that it shows clearly that the inward extension of the 
endodermis is evident before the external endodermis 
is interrupted (Text-fig. 1 , a, b). In other cases this 
may not be obvious. The most natural way of re- 
garding the extension of the endodermis seems to 
be as an assumption of endodermal characters by 
certain intrastelar cells and not as indicating an in- 
trusion of cortex. This is more clearly shown in 
Text-fig. 2, which represents the departure of one 
of the earlier traces of plant A (cf. Text-fig. 3). In 
this case the new formation of endodermis appears as 
a reparatory band, completely bridging across the gap 
before the trace has actually separated. There is thus 
never an open gap in the endodermis. The adult type 
may be placed in relation to this by regarding the new formation of 
endodermis to either side as corresponding to an incomplete reparatory 
band. These two types of leaf-trace departure do not exhaust the variety 
of endodermal relations found at the leaf-gap in B. Lunaria. Other 
examples where the process is complicated by the presence of an internal 
Text-fig. 2. Endo- 
dermal relations in the 
departure of a leaf- trace 
with no gap in the external 
endodermis. Description 
in text. 
