218 BOTANICAL GAZETTE [SEPTEMBER 
with walled cells. Four of the 6 cells in Actinostrobus organize 
as embryo initials and give rise to embryos. Neither ARNOLDI 
(1) nor Lawson (22), in their work on Sequoia, followed the 
embryo development very far. They probably studied the develop- 
ment of only a single embryo from each egg. It seems prob- 
able that the other 3 cells which are cut off by walls in the first 
2 divisions of the proembryo of Sequoia may represent embryo 
initials, and more careful study may perhaps reveal secondary 
embryos arising from 1 or more of these other 3 cells. Like 
the rosette embryos in Pinus, these possible secondary embryos 
in Sequoia may develop only after some delay, and thus easily be 
overlooked. Actinostrobus, and possibly Sequoia, represent forms 
in which cleavage polyembryony has been retained more or less. 
The cleavage polyembryony of Pinus suggests an explanation 
of the proembryo of Ephedra, described by STRASBURGER (38) and 
LAND (21). Here the 8 free nuclei of the proembryo organize 
with walls as embryo initials, and from 3 to 5 of them produce 
embryos. The embryo initials organize only at the bottom of 
the egg in Pinus, while in Ephedra they organize with walls before 
reaching the bottom. Ephedra has thus retained, in a modified 
form, a very ancient character, that of cleavage polyembryony, @ 
character which indicates that this plant has descended from the 
Coniferales. According to the testimony of their embryogeny, 
such forms as Pinus and Actinostrobus must be looked upon as the 
nearest conifer relatives of Ephedra. 
A comparative study of conifer embryos suggests several possible 
evolutionary lines of advance. One of these is the one beginning 
with Pinus and culminating in Ephedra, in which cleavage poly- 
embryony is retained in some modified form. The apical cell 
feature is retained among the more primitive embryos of this line, 
but apparently lost by the time the Ephedra level is reached. 
The abietineous embryo of the type represented by Picea (38) 
would be produced when all the embryo initials together develop 
1 embryo. Here the lower tier is an even one, and if the embryo 
develops uniformly a meristematic group of 4 cells replaces the 
apical cell from the first. Thus Picea may represent the culminating 
abietineous embryo type, while Pinus represents the primitive type. 
