EMBRYO DEVELOPMENT AND POLYEMBRYONY 
ony. A few stages in this araucarian line of evolution may be illustrated by 
Sciadopitys and the podocarps. 
SCIADOPITYS 
The embryogeny of Sciadopitys (figs. 10-15) has been partially described 
by Lawson (27) and Arnoldi (i), and represents a step in the direction of 
Araucaria. There are at least eight free nuclei before walls form (see fig. 
10), and Lawson states that ''eventually the proembryo consists of three 
tiers of cells and one tier of free nuclei," from which I have supplied fig. 11. 
However, the organization of embryo initials continues in the terminal tier 
Figs. 10-15. Stages in embryogeny of Sciadopitys. Figure 10 after Lawso n (27) 
figures II and 12 supplied from description by Lawson; figures 13-15 after Arnoldi (i). 
until a group of about 16 cells is formed (fig. 12). (This stage is also 
supplied from Lawson's description and from a study of the next stage (fig. 
13) by Arnoldi.) Finally the suspensor tier elongates and thrusts the 
terminal group of cells into the gametophyte, a stage shown in figure 13. 
That the cells of this terminal group are really embryo initials, mostly 
advanced to the two-celled stage, is borne out by the next two figures. 
It will be noted that in Sciadopitys a large number of embryo initials 
are produced, and the functional ones are organized in this instance after 
the first walls have formed in the proembryo; that is, the lowest functional 
group is not the first group of embryo initials to organize, as in Pinus, but 
the last. I would look upon a late organization of the functional embryo 
initials from previously walled cells as a more advanced condition, for this 
occurs quite generally in the more recent conifers. 
Rosette embryos undoubtedly exist in Sciadopitys, as Lawson accounts 
for walled cells above the suspensor, and Arnoldi definitely described a 
group of proliferating cells occupying this position which he noted as a 
possible vestigial protocorm, comparable to the protocorm of lycopods. 
He states: '*Ich kann gewiss nicht bestimmt entscheiden, ob es ein 
morphologisches Gebilde ist, oder eine Anpassung zur noch weiteren 
Polyembryonie." Unfortunately Arnoldi gave us no figures of this "proto- 
corm," but it is probably safe to infer that he saw a group of rosette embryos, 
and that the entire embryogeny of Sciadopitys represents a modification 
in the direction of greater cleavage polyembryony. 
