Embryo and of that of the Grass in particular. 519 
evidence for such a thing, nor can any logical reason be given for supposing 
such a modification to have occurred. There is, on the contrary, plenty of 
evidence, some of which has been given above, for holding the opposite 
view, viz. that the cotyledon is primitively terminal. 
A very important matter has yet to be referred to. It concerns the 
relative degree of development of the lamina and the sheath of the cotyledon 
in Monocotyledons. In the majority the lamina greatly overreaches in 
development that of the sheath. In the Dioscoreaceae and Commelynaceae, 
as Celakovsky points out, the state of affairs as described by Solms- 
Laubach is due to the fact that the sheath has developed at an earlier stage 
than, and consequently ahead of, the lamina (Fig. 10, A-c) ; the apical 
portion of the embryonic thallus has been used up to form the sheath , which 
appears in the form of a circular outgrowth ; there is no shoot-grozving- 
point present until a later stage ; the lamina arises subsequently as a 
lateral outgrowth of the sheath. 
Wherever in Monocotyledons the appearance of a second cotyledon is 
found, it can be traced to a special development of the cotyledonary sheath 
or of the basal portion of the lamina, which inevitably suggests a peripheral 
or lateral position of the one or two cotyledons. This it is which has mis- 
led Coulter into imagining that in the Grass-embryo either two or one, as 
the case may be, lateral cotyledons are present. The appearance is simply 
due to the very special development of the lamina of the cotyledon as a haus- 
torium and of its basal region in the form (where present) of the epiblast. The 
latter organ Celakovsky has shown to correspond to modified appendages 
of the lamina of the cotyledon ; the development shows that the coleoptile 
is the ligular portion of the cotyledon, and that the whole arises as a single 
organ, on essentially the same lines as in other Monocotyledons, before any 
other leaves or any trace of a stem-apex is present. Under these conditions 
it can be nothing else but terminal. Coulter himself states that no stem-tip 
is present even at quite a late stage. In the absence of a stem how is 
it possible, I ask, for the cotyledon or cotyledons to be peripheral or 
lateral ? Peripheral or lateral to what ? What is this ‘ peripheral zone 5 he 
mentions from which the supposed two cotyledons arise on opposite sides ? 
It must be one of two things. : either (1) the earliest stage of the two first 
leaves (cotyledons) whose bases are united to form a sheathing structure, 
and whose position, of course, must be lateral to a stem ; or (2) it repre- 
sents a single cotyledon with its well-developed basal portion. Now 
(1) cannot possibly be the explanation, for at that stage there is a complete 
absence of any stem to which the cotyledons could be lateral ; for it 
is an absolute impossibility for two distinct cotyledons to exist without any 
axis to which they are attached. Hence (2) must be the true explanation, 
is any trace of an epicotyledonary axis ; hence they cannot be two lateral cotyledons, but a single 
bifid terminal one. 
N n 2 
