4 Sargant. — Theory of the Origin of Monocotyledons 
of a theory on the origin of Monocotyledons, founded primarily 
on the structure of their seedlings, and supported by the com- 
parison of this structure with that of some Ranunculaceous 
genera in which the cotyledons are more or less completely 
united. 
The argument requires that some weight should be given 
to the vascular system of the seedling as affording indications 
of its race-history. This postulate stated, I will briefly sketch 
the theory I have formed, and indicate the nature of the 
evidence on which it rests, before proceeding to give the 
evidence itself in greater detail than was possible in a pre- 
liminary notice. 
The study of Liliaceous seedlings has led me to the con- 
clusion that the various types of vascular symmetry found 
within the order can be linked with the type found in 
Anemarrhena , Albuca , and Galtonia , through more than one 
series of intermediate forms. I regard the Anemarrhena type 
as primitive, and as the starting-point from which most, if not 
all, the vascular types characteristic of Liliaceous seedlings 
have been historically derived. 
The cotyledon of Anemarrhena contains two massive bun- 
dles which together form a tetrarch stele in the primary root. 
This structure originally suggested to me the possibility of 
a fusion of two seed-leaves in some remote ancestor to form 
the single cotyledon of Anemarrhena. According to this 
view each bundle in the hypocotyl represents the trace of one 
seed-leaf. 
The seedlings of certain Dicotyledons possess seed-leaves 
which are partially united, sometimes by one margin only, but 
more often by both. In the latter case the united petioles form 
a tube, which is sometimes of considerable length. Petiolar 
tubes of this kind are found in several species of Anemone 
and Delphinium ; in two species at least of Ranunculus and 
one of Trollius ; in Aconitum Author a and Eranthis hiemalis. 
The authorities for these statements will be found in Part II. 
Many other genera among the Ranunculaceae have cotyle- 
dons which are concrescent at the base. The petiolar tube 
