159 
Primitive A ngio sperms. 
Suppose, on the other hand, that the Primitive Angiosperms possessed 
two cotyledons. They may have been reduced to one in living Mono- 
cotyledons by either of two methods. One of the pair may have been sup- 
pressed, or both cotyledons may have fused into one. That the change from 
a dicotylar to a monocotylar embryo can be effected without difficulty is clear 
from the existence of pseudomonocotyledons — species with a single cotyledon 
belonging to widely separated Dicotyledonous genera. In each genus the 
reduction of two cotyledons to one has taken place independently. We 
have seen that the development of the embryo within the embryo-sac gives 
no clue to the method by which such reduction takes place — at least in 
the three species investigated. 
Vestiges of a second cotyledon opposite the functional one have been 
sought in vain by many observers ; Hegelmaier believed he had found 
such a rudiment in the abnormal embryo of Carum Bulbocastanum already 
mentioned. Little weight need be attached to an isolated instance of this 
kind. The epiblast of certain Grass embryos has been interpreted as a rudi- 
mentary cotyledon (Van Tieghem), but this view is not generally accepted. 
Little evidence has so far been brought forward in favour of the third 
and last possibility, that of the fusion of both cotyledons of the Primitive 
Angiosperm into a single member. Sterckx attributes the bilobing of the 
embryo in Ranunculus Ficaria to an origin of this kind, but even if his 
arguments were conclusive they would not decide the question in the case 
of true Monocotyledons. 
To sum up, comparison with Gymnosperms establishes a presump- 
tion in favour of two cotyledons among the Primitive Angiosperms. The 
development of the embryo within the embryo-sac gives no decided clue 
to the ancestral form. The shape of the whole structure and the sequence 
of its development seem far more dependent on the environment than on 
inheritance of ancestral features. 
One class of evidence is as yet untouched — the history of the embryo 
after germination. The embryo is less cramped when it has escaped from 
the seed, and the development of vascular tissue gives rigidity to its form. 
Ancestral features if reproduced after this epoch stand a better chance of 
being preserved. 
Embryology after Germination. 
The anatomy of seedlings cannot be understood apart from their 
external characters. On germination the outline of the embryo is much 
altered, but this depends not on the formation of new members but on 
changes in the proportion of those already present to each other. This is 
quite clear in the familiar examples of germination — bean, acorn, maize. 
The exit of the radicle and plumule from the seed is commonly due to the 
basal elongation of the cotyledon or cotyledons. This elongation is followed, 
