Ethel Sargant . 
107 
THE ORIGIN OF THE SEED-LEAF IN 
MONOCOTYLEDONS. 
By Ethel Sargant. 
T is now five years since I began the study of the vascular 
system in Monocotyledonous seedlings. My object from the 
first was to throw light on the race-history of Angiosperms. A 
general probability is acknowledged that systematic characters 
drawn from the structure of the embryo possess, in plants as in 
animals, a special claim to attention. The study of vegetable 
embryology has, however, been hitherto singularly barren of such 
results, and has yielded but one character of systematic value. 
The presence or absence of endosperm in the ripe seed, though an 
important character, can hardly be considered as strictly embryonic. 
The number of the seed-leaves in the embryo is the single 
character to which I have referred as of acknowledged systematic 
value. The fundamental division of the Angiosperms is that which 
separates plants possessing one seed-leaf from those possessing 
two. The other characters which distinguish Monocotyledons from 
Dicotyledons are merely corroborative, and are subject to many 
variations. 
Recent research has tended to show that the Angiosperms are 
a very well-defined group, separated from all others by the 
possession of a true endosperm—that is, a food-body, formed after 
fertilization, within the embryo-sac, independently of the embryo, 
but side by side with it. The breadth of the gulf separating the 
Angiosperms from the Gymnosperms and higher Pteridophytes can 
hardly, in the present state of knowledge, be attributed entirely to 
our ignorance. There must be a real absence of intermediate 
groups, though we may hope to discover some stray forms, living or 
fossil, which may indicate how in past ages that gulf was bridged. 
When we realize the isolation of the Angiosperms, the dividing- 
line between the two main groups into which they fall appears less 
marked than before. The common ancestor of Monocotyledons 
and Dicotyledons may have been quite unlike any existing species 
of either class. It may have combined features from both, and yet 
have been an undoubted Angiosperm. It almost certainly possessed 
either one or two seed leaves. If the former, the Monocotyledons 
must be considered the more ancient group; if the latter, the 
Dicotyledons. 
