SMITH: DIOSCOREA VILLOSA 549 
duced: by this division in Dioscorea villosa are usually of about the 
same size (F1G. 4), but sometimes the basal cell is larger (F1G. 2). 
On account of the flattened shape of the seed it is possible to 
section the ovules always in the same plane. All figures of sec- 
tions of the embryo are drawn from median longitudinal sections 
which are vertical to the plane of the cotyledon and which con- 
sequently afford a fair basis for comparison. In no case is a large 
vesicular basal cell formed, such as has been described in the 
embryos of the Najadaceae and Alismaceae. 
The second division occurs in the basal cell, at right angles to 
the first wall (Fic. 3). Next, the terminal cell divides (Fic. 4); 
the position of the wall formed as a result of this division varies: 
in some embryos it is in the same plane as that of the second 
division (Fic. 4); in others, it is at right angles to the second wall, 
as in the embryo shown in Fie. 5, in which the third wall is nearly 
in the plane of the section and therefore cannot be shown in the 
figure. By either method, four similar cells are formed, as is the 
case in a few monocotyledons which have a massive proembryo 
rather than one of the filamentous sort that was formerly con- 
sidered typical for the class. Quadrant formation has been ob- 
served in three genera of monocotyledons, Lysichiton (Campbell 
1900), Lilium (Coulter, 1897), and Erythronium (Schaffner, 1901). 
It can hardly, however, be considered typical for the Dioscoreaceae, 
since in Tamus communis (Solms-Laubach, 1878) a filamentous 
three-celled proembryo has been described. 
The next division may take place in one of the two distal 
cells or in one of the two basal cells. In the embryo shown in 
Fic. 5, the nucleus of one of the distal cells of a four-celled embryo 
is dividing; the wall separating the two distal cells is, as already 
noted, so nearly parallel to the plane of the section that it cannot 
be indicated in the figure. The spindle is at a lower focus than 
the resting nucleus shown. 
In most cases, the second of the two distal cells of the four- 
celled stage now divides, so that a six-celled embryo is formed. 
Up to this time the embryo has not materially increased in size, 
but from now on there is a gradual growth. At the eight-celled 
stage (Fic. 6) the embryo is already noticeably larger, the size 
of the individual cells at this time being approximately equal to 
