6 Sargant . — Theory of the Origin of Monocotyledons 
common ancestor : or as the response of two unrelated forms 
to similar conditions. 
The formation of a tetrarch root-stele from two cotyle- 
donary traces is not common among Monocotyledons. It is, 
I believe, unknown among Dicotyledons. The indications of 
such a tetrarch formation in Eranthis are to my mind very 
clear — I cannot dismiss them as accidental. This considera- 
tion leads me to believe in a real genetic connexion between 
Eranthis and Anemarrhena : that they are descended from 
a common ancestor with two distinct seed-leaves, each repre- 
sented by a single trace in the hypocotyl. If we suppose 
that this is in its turn descended from a form in which two 
traces enter the hypocotyl from each cotyledon, the tetrarch 
root will no longer present any difficulty. 
But even if there be no historical connexion between these 
genera, the structure of Eranthis may nevertheless illustrate 
the double origin of the Anemarrhena cotyledon. For with- 
out the analogy of Eranthis the assumption that each trace 
in the cotyledon of Anemarrhena represented a distinct seed- 
leaf was groundless. Not only was direct evidence of such a 
double origin absent, but there was nothing to show that the 
union of two cotyledons, if it did take place, would actually 
give rise to such a type of vascular symmetry. To settle the 
matter by experiment was out of the question. But in 
Eranthis the cotyledons are partially united, and the vascular 
symmetry bears a very close resemblance to that of Anemar- 
rhena. If there is no common stock from which both forms 
are derived, Eranthis may be considered as a genus in which 
Nature has partly repeated the experiment which she con- 
cluded in Anemarrhena , and with a similar result as regards 
the vascular system. 
This is the line of argument on which my theory is based, 
and it remains now to give a fairly full abstract of the 
evidence which supports it. I propose to do so under two 
heads. 
In the first place I shall describe the chief types of vascular 
symmetry which have so far been found within the Liliaceae, 
