1898] EMBRYOLOGY OF ALYSSUM 315 
except from very young buds, to insure rapid penetration. 
Chrom-acetic acid, and a solution of corrosive sublimate, acetic 
acid, and 70 per cent. alcohol were the two fluids used. For 
general purposes the first seemed preferable, though satisfactory 
results were obtained from both. 
The material was imbedded in paraffin and cut into sections 
124 thick. It was difficult to orient the ovaries so as to get 
sections parallel to the plane of the embryo sac, since the 
ovule of Alyssum is campylotropous and the embryo sac soon 
becomes curved like a horseshoe nearly parallel to the septum 
of the silicle. 
Anilin-safranin, alone or in combination with gentian violet, 
and sometimes with a third, orange gentian, was used in stain- 
ing. Acid fuchsin and iron-alum-hematoxylin were also 
employed. The latter was very useful in bringing out early 
Stages of the embryo sac, but it was not so good after endo- 
Sperm was present. Combinations with anilin-safranin were most 
Satisfactory for general purposes. 
A Bausch & Lomb microscope with 2, 4 and ;'; objectives, 
and 2 and 1 inch oculars, was used, and drawings were made 
with the aid of a Bausch & Lomb camera. 
DEVELOPMENT OF MACROSPORES AND EMBRYO SAC. 
The archesporial cell (fig. 7) is hypodermal in origin and 
can be recognized in the nucellus before the two outer integu- 
ments have entirely surrounded it. The nucleus of the arche- 
sporial cell is larger than those in other cells and the contents 
are more granular. By a transverse division a tapetal cell (Ag: 
2,¢) is cut off, and this apparently undergoes no further division. 
The macrospore mother cell, however, divides into four cells, 
three potential macrospores (jig. 2, /) and a vital macrospore 
(jig. 2, m), which is the lowest of the series and develops into 
the embryo sac, destroying the entire nucellus in its grow 
( figs. 2-12). : hone 
The two-celled embryo sac (fig. 3) is nearly straight, with 
nuclei at Opposite extremities and a well marked vacuole in the 
