EMBRYO DEVELOPMENT AND POLYEMBRYONY 
Sinnott (39) described P. totara and P. nivale as producing walls at an earlier 
stage, which fact places the Podocarpineae a little closer to the Abietineae. 
Coker states that either the embryo may split up or its parts may unite 
in producing the embryo, but it is highly probable that cleavage poly- 
embryony is the normal condition in the species which he investigated. 
All his figures of embryos that presumably were produced by simple poly- 
embryony appear very much like those which one would expect to see in the 
older separated embryos which have a secondary suspensor, and we know 
that all conifers produce such secondary additions to the suspensor by the 
elongation of cells to form embryonal tubes. From the interlocking articula- 
tion of the embryo of figure 21a with its suspensor, it is evident that these 
are embryonal tubes and not the primary suspensor, as inferred by Coker; 
but the largest embryo of this group is not the terminal one in this particular 
instance. 
It is also possible that the apical cell stage is found in these separating 
embryos of Podocarpus, as may be seen by a careful study of figures 21-24. 
No rosette cells are found in the above described species (I refer to walled 
rosette cells, not the free nuclei that abort above). 
In Podocarpus nivalis, Sinnott described and figured a thick cellulose 
cap "protecting" the binucleate terminal cell, as shown in figure 23, which 
is pushed far into the gametophyte before it divides further, and ''instances 
of budding or of single suspensors giving rise to embryos were only rarely 
observed." Does it not appear that this thick cellulose cap would tend to 
prevent a splitting of the embryo and so to cause the initial cells of the 
lower tier to combine and produce a single embryo? 
I have occasionally observed a cap of wall thickening which appeared 
to hold together the terminal cells in the embryo of Pseudotsuga,^ but this 
structure is not found in the slightly later stages. It is evident that cleavage 
polyembryony occurs only with considerable difficulty where such a thick 
cellulose cap protects the terminal group of cells. I am inclined to look 
upon these caps as mechanical devices which prevent cleavage poly- 
embryony. 
Another type of embryo development, probably a higher specialization 
of that above described, is also found in the Podocarpineae. I refer for 
illustration to the embryo of Podocarpus spicatus (figs. 25-26), one of the 
Stachyocarpus group (39), in which the terminal cells organize into a cap 
while the cells above the cap give rise to a single embryo and its suspensor 
of embryonal tubes. In this case we have no cleavage polyembryony, 
and it appears that the function of this cap, which is soon sloughed off, 
may be to prevent this splitting of the embryo, a danger present only in the 
first stages. However, it would probably not prevent cleavage polyembry- 
ony as successfully as the more elaborate caps found in Araucaria and 
Agathis. 
3 Unpublished work. 
