146 
Sargant . — The Reconstruction of a Race of 
The question is whether Primitive Angiosperms had one cotyledon 
or two. Evidence of two kinds is available. Living Angiosperms may 
be compared with other groups. If the number of cotyledons found among 
lower plants, living or extinct, be at all constant, there would be some 
reason to suppose that number to be derived by Primitive Angiosperms 
from their ancestors. 
In the second place, there is embryological evidence. The develop- 
ment of the embryo in both classes may perhaps repeat its race-history 
in some degree. Many observations have been made on the development of 
the embryo within the embryo-sac, that is, on the period in the history of the 
young plant which begins with the division of the fertilized ovum and ends 
with the formation of the ripe seed. The next period commonly begins 
with germination. The embryo of the ripe seed has merely to elongate 
its members and push them out of the seed-coats in order to become the 
seedling. 
But this is not always so. In a considerable number of species be- 
longing to both classes, but particularly numerous among Monocotyledons, 
the embryo passes through a period of maturation between the ripening 
of the seed and its germination. In such species the embryo is not ready 
for germination by the time the seed is ripe ; it resumes its growth within 
the embryo-sac when sown under proper conditions. Seeds containing 
such embryos lie dormant in the soil for months after they have ripened 
and been shed from the plant. Germination is of necessity postponed until 
the embryo is fully differentiated. 
For our present purpose, however, the epoch of germination is the 
most convenient division. The embryological evidence will be considered 
under two heads : the development of the embryo within the embryo-sac, 
whether that development is complete within the ripe seed or not, and the 
development of the seedling after germination. 
Let us begin by comparing Angiospermous cotyledons with those 
of other plants. The Gymnosperms alone possess cotyledons which are 
clearly equivalent to them. Among Gymnosperms two cotyledons are 
found in the Cycads, in the Gnetaceae, in the extinct Bennettiteae, in 
Gingko , the Cupressineae, and the Taxaceae. More than two are found 
among most Abietineae and Taxodineae. The Araucarieae differ. Agathis 
has two cotyledons, Araucaria two to four. 
Two cotyledons, then, are very frequently found among Gymnosperms. 
One is unknown, unless it occur in Ceratozamia} The more primitive forms, 
such as the Cycads and Ginkgo , have two. So have the Gnetaceae and 
Bennettiteae, two groups which in other characters approach Angiosperms. 
With the exception of the poly-cotyledonous Araucarias , those groups which 
1 Eichler (22), p. 1 7 . 
