174 Sargant . — The Reconstruction of a Race of 
cotyledons and rather rare among Dicotyledons, but quite a large number of 
Monocotyledons have net-veined leaves. Again, the three-fold symmetry 
of the flower is quite characteristic of Monocotyledons, but some Dico- 
tyledons display it, while many Monocotyledons have whorls of four 
or even five parts. So with other characters, such as the short-lived 
primary root of Monocotyledons and their albuminous seeds. Though no 
one of these minor characters can be used as a test in the same way as 
the stem-anatomy or the number of cotyledons, yet collectively they do 
separate Monocotyledons from Dicotyledons very completely. 
This consideration suggests another way of attacking the whole problem. 
Whichever view we take, for example, concerning the number of cotyledons 
possessed by the Primitive Angiosperms, whether with Professor Lyon 
we suppose it monocotylar, or dicotylar with Professor Henslow, one branch 
of its descendants must be considered as inheriting the original character, 
and the other as modified in that respect. If the seedling of Primitive 
Angiosperms was monocotylar, then the two cotyledons of Dicotyledons 
were developed from the single ancestral member. If the Primitive Angio- 
sperms had two cotyledons, then the single member of Monocotyledons 
is the innovation. 
In either case some cause must have existed for the change. The 
variations in that direction would not have survived had not circumstances 
prevailed under which the new structure was in some respects preferable 
to the old. And it is probable that some of the other characters now 
associated with the possession of one cotyledon, or of two, were differentiated 
in response to the same circumstances. 
We may, then, inquire whether any causes have been suggested to 
account for the formation of two cotyledons from one or one from two. 
And if more than one view has been advanced, which of them would best 
explain the correlation of stem-anatomy and minor characters with the 
derived form ? 
To begin with the theory of a primitive single cotyledon giving rise 
to a pair by fission, how does it stand this test ? Professor H. L. Lyon 
is the most recent exponent of this view. His papers (57, 58) are remark- 
able for the precision of their statements, and for the unflinching way 
in which he faces the theoretical consequences of his views. But the only 
hint given as to the cause of the fission by which one cotyledon becomes 
two is the suggestion that a bifid cotyledon might be of use to the embryo 
while it is getting clear of the seed. No attempt is made to correlate the 
stem anatomy of Dicotyledons, or any of their minor characters, with 
the dicotylar form of their seedlings. 
This omission is not peculiar to Professor Lyon. The monocotylar 
theory has been accepted by most botanists for more than a generation, 
