■Ian., 1903.] 
( Uaytonia virginica. 
349 
THE DEVELOPMENT OF THE EMBRYO-SAC AND 
EMBRYO OF CLAYTONIA VIRGINICA * 
Melville Thurston Cook. 
Claytonia virginica Linn, was selected as a type for class study. 
The number of interesting points led me to complete the series of 
preparations and prepare the results for publication. The wide 
distribution and the ease with which the material can be killed 
and prepared for class work may make it an equally desirable 
type for others who may wish to study a dieotyl with unequally 
developed cotyledons. 
METHODS. 
The material was killed and fixed in Fleming’s solution, passed 
through the alcohols, imbedded in paraffin and cut on a Minot 
microtome. In most cases the sections were cut rather thick. 
For the very \ oung stages only the calyx was removed. The 
fluid will penetrate the ovules readily until they are old enough 
to change their color from white to brown or black ; after that it 
is necessary to puncture the integuments. A combination of 
anilin safranin and gentian violet gave the best results. 
MEGA SPORES AND EMBRYO-SAC. 
The single arehesporial cell is hypodermal in origin, and can be 
easily recognized from the surrounding cells of the nueellus. 
From this a single tapetal cell is formed, which may divide again 
either by anticlinal or pericliual w'alls (Figs. i. 2 (>). In § very 
few cases three tapetal cells were observed (Fig. 2 b). Four 
megaspores are formed in the usual manner (Figs. 2 a. 2d). The 
lower or functional megaspore enlarges at the expense of the three 
potential megaspores and the tapetal cells (Fig. 3). The func- 
tional megaspore now enlarges, giving rise to the two, four and 
eight celled embryo-sac in the usual manner ( F'igs. 4, 5, 6, 8). 
In the four-celled stage the nuclei are approximately equal in 
size. In the eight-celled stage the synergids are very large and 
pear-shaped, and at least one persists until a very late stage in the 
development of the embryo (Figs. 9, 10, 12, 13, 14, 16, 18). The 
egg is slightly larger than the synergids and very similar in 
appearance ; while the polar nuclei are comparatively large (Figs. 
6, 7). The antipodals are somewhat smaller and cut off from the 
sac by delicate but definite walls (Fig. 6), and always occupy 
about the same relative position to each other. 
* Contributions from the Botanical Laboratory of Ohio State University. X. 
