136 
JOHN T. BUCHHOLZ 
Taxads 
The taxad line may have been derived from some of the podocarps, 
or more probably along with these from a condition nearer to that of Pinus. 
In Taxus (i8) there are at least i6 free nuclei before walls form, and the 
terminal tier of the proembryo may contain several cells, probably all of 
Figs. 37-40. Stages in embryogeny of Taxus haccata, X 125, Fig. 37. Proembryo 
at beginning of suspensor elongation, after Hofmeister (17). Fig. 38. Slightly later stage. 
Figs. 39 and 40. Later stages showing apical cell in early embryo. Figures 38-40, after 
Strasburger (40). 
them potential embryo initials. Apparently one of these several cells, 
doubtless the one most favorably situated, begins to cut off apical cell 
segments and gains the ascendency over the others (40), which in turn 
contribute by their activity to the suspensor. Figures 39-40 by Strasburger 
(40) show that the apical cell persists for some time, and this furnishes an 
instance of the elimination of cleavage polyembryony with the retention of 
the apical cell. 
According to Jager (18), some of the upper suspensor cells of Taxus 
may occasionally break away and appear to give rise to small secondary 
embryos, but practically always the proembryonic cells all combine into a 
single embryo. Thus, Taxus _ baccata appears to have practically overcome 
cleavage polyembryony, but still shows some vestigial evidence of an origin 
from this condition. In commenting on this Jager (page 182) makes the 
significant statement that it appears to him that occasionally all the cells 
of the early proembryo show a capacity for giving rise to embryos, and in 
this statement he seems to have approached very close to the present 
explanation. 
In Torreya, the proembryonic tissue fills the entire egg, while in Taxus 
it is confined to the lower portion of the egg. Torreya has only four free 
nuclei before walls form, and, though no cleavage polyembryony occurs, the 
vestigial evidence of it in the form of occasional secondary embryos has 
been described (14). The differences between Taxus and Torreya may be 
looked upon as due to higher specialization of the latter, and it is therefore 
questionable if the apical cell stage exists in Torreya. 
