70 Sargant . — Theory of the Origin of Monocotyledons 
ment contradicts the theory of its double origin, but I doubt 
whether that origin would have been suggested by the struc- 
ture of the embryo at any period had the union of the 
cotyledons in the mature organ been more perfect. 
Finally, Count Solms-Laubach ( 37 ) has shown that the 
cotyledon is not always apparently terminal in the embryo of 
Monocotyledons. In several genera belonging to the Com- 
melinaceae, and in Tamus communis , the plumule is terminal 
from the moment of its appearance, and the single seed-leaf 
lateral. Its development in these species resembles that 
of the cotyledonary member in Ranunculus Ficaria. 
These considerations are sufficient to throw doubt on the 
theoretical conclusions drawn by Mr. H. L. Lyon ( 31 ) from 
his interesting observations on the development of the embryo 
in a single species of Nelumhium . Professor Strasburger 
( 39 , p. 510) has pointed out that the apparently lateral position 
of the growing-point described by Mr. Lyon in this species is 
probably due to the position of the embryo within the embryo- 
sac, and that the same cause might bring about the early 
fusion of both cotyledons into a single rudiment, though they 
are later quite distinct. 
2. Homology of the Seed-leaf in Monocotyledons. 
Assuming that the seedling with one seed-leaf is derived 
from an ancestor with two, the change may have come about 
in one of two ways. One cotyledon of the pair may have 
been suppressed by degrees, or both have united to form 
a single member. 
The first alternative is that adopted by Mr. Henslow in 
1892 ( 15 ). It has commonly been regarded as the only 
working hypothesis by the botanists who have seriously 
considered the possibility of deriving Monocotyledons from 
a Dicotyledonous stock. 
When in 1902 I published a short paper in the New 
Phytologist ( 35 ) giving an abstract of the reasons which 
led me to the conclusion that the single * cotyledon ’ of Mono- 
cotyledons was derived from both the cotyledons of a remote 
