1909] MCALLISTER—EMBRYO SAC OF SMILACINA 203 
chromic acid 0.7%, glacial acetic acid o.5°°, water 100°°. A fixative 
composed of two parts absolute alcohol and one part glacial acetic 
acid gave very good results also. Flemming’s weak solution was not 
tried. 
Smilacina stellata is especially favorable for obtaining a complete 
series of stages of the early development of the embryo sac. The 
flowers, eight to fourteen in number, are borne in a raceme, which 
does not expand till the embryo sac has nearly reached the eight- 
celled stage. It is therefore possible to cut an entire’ raceme longi- 
tudinally and get a maximum number of ovules cut parallel to their 
long axes. The oldest flowers are at the bottom. Each flower con- 
tains five to seven ovules, and about seventy racemes were cut in 
paraffin. ; i 
In the material collected November 16, the nucellus was only 
partly developed in the lower flowers of the raceme. There were 
no mother cells to be distinguished in any of this material. Material 
collected May 7 showed, in a few shoots, mother cells in the synapsis 
stage in the lower flowers, while at the top of the shoot the nucellus 
was barely differentiated. Most of the racemes taken at this date 
Were farther developed: than those mentioned above, the younger 
flowers being at least in the synapsis stage. 
The mother cell is located at a variable depth beneath the surface 
of the nucellus. Not uncommonly it is immediately beneath the 
epidermis (fig. 1). In other cases it is separated from the epidermis 
by one cell layer. Most commonly two cell layers intervene (fig. 2). 
Measurements of several camera drawings of the mother cell at the 
Synapsis stage gave an average breadth of 22 #, and an average length 
of 30 Bb. ’ 
I shall not here take up in detail the question of the reduction of 
thechromosomes. In the first division of the mother cell, thick double 
chromosomes, characteristic of the metaphases of the heterotypic 
division, appear (fig. 3). The number of bivalent chromosomes, 
as shown in the anaphase stage of this division, is twelve. The 
‘porophytic number, as shown by root tip cells, is twenty-four. - 
A definite cell plate, and in most cases a cell wall, is formed, 
Separating the two daughter nuclei of the first division before the 
‘econd division takes place (figs. 4, 5). The cell plate is formed by 
