EMBRYO DEVELOPMENT AND POLYEMBRYONY 
In the Podocarpineae and Cephalotaxus, the functional initials were reduced 
by the abortion of a large portion of the free nuclei in the proembryo, 
the walled cells below these became suspensor-like, and cleavage poly- 
FiGS. 33-35. Stages in embryogeny of Agathis australis. Fig. 33. Proembryo after 
wall formation, X 200. Fig. 34. After cap is formed and suspensor begins to elongate, 
but before archegonium is filled, X 260. Fig. 35. Section through tip of older embryo 
showing the small cells below the suspensor from which the embryo is derived, X 460. 
After photomicrographs by Fames (15). Fig. 36. Embryo of Araucaria brasiliensis, 
drawn to half the scale of figure 35, X 230. After photomicrograph by Burlingame (5). 
embryony was eliminated by the organization of caps of various kinds; 
while in the Araucarineae all the free nuclei are utilized and become organ- 
ized into an embryo whose terminal portion has a multicellular cap, as 
shown in figures 33-36. 
These embryos of Agathis and Araucaria were very satisfactorily de- 
scribed by Eames (15) and Burlingame (5), and neither of these investigators 
found cleavage polyembryony. In both these species the free nuclear 
divisions of the proembryo are essentially the same. The proembryo is 
confined to a samll portion of the egg cytoplasm, and the embryo has begun 
to elongate considerably before the archegonium is filled by its tissue. 
The entire embryogeny of the Araucarineae bespeaks a high degree of 
specialization. 
That the cap is not particularly useful in protecting the embryo in its 
penetration of the gametophytic tissue was brought out by Burlingame (5), 
and the possibility that it is a special secretive organ is just as remote; but, 
since other conifers appear to have developed mechanical devices to prevent 
cleavage polyembryony, an explanation of this nature is possible. 
An explanation which would derive the Abietineae from the Aracuarineae 
on the basis of embryogeny is beset with great difficulty, if not impossible; 
but it is not so difficult to show how the araucarian embryo has developed 
from a form very similar to that of Pinus as a specialization along a par- 
ticular line. At the same time this latter theory offers a satisfactory 
explanation for the nature of the cap. 
