Feb., 1903 .] 
Agrostemma githago. 
3 6 5 
THE DEVELOPMENT OF THE EMBRYO-SAC AND 
EMBRYO OF AGROSTEMMA GITHAGO.* 
Melville Thurston Cook. 
Agrostemma githago L. was selected as a plant for comparison 
with Claytonia virginica, they usually being placed in the same 
order but in different families. 
The ease with which the material can be prepared and the reg- 
ularity of the development of the embryo-sac and embryo make 
it a very desirable plant for study. 
METHODS. 
The material was killed and fixed in Flemming’s solution and in 
chromo-aeetic, passed through the alcohols, imbedded in paraffin, 
cut on a Minot microtome and stained in aniline safrauin and 
gentian violet, and also in Hadenhaine’s haematoxy din and iron 
alum. For the development of the embryo-sac the safranin and 
gentian violet combination was most desirable, but for the devel- 
opment of the embryo either stain was satisfactory. 
The young buds were killed entire, but the sepals and petals 
were removed from the older ones. In the very youngest stages 
it is desirable to cut the sections thin, but when the embryo-sac 
has reached the eight-celled stage it must be cut thick, otherwise 
important structures may be lost. The orientation was very 
simple ; by cutting the ovaries transverelv the sac will be cut 
longitudinally. 
The archesporium may originate as one, but more frequently 
as two or three, liypodermal cells (Figs, i, 2, 3). These increase 
in size (Fig. 2), and one eventually absorbs the others. Many 
specimens were examined, but in all cases only one cell developed 
into an embryo-sac. This single arehesporial cell now divides by 
transverse divisions into three cells, of which the lowest develops 
into the functional megaspore (Fig. 4.) The two (Fig. 5), four 
(Fig. 6), and eight (Fig. 7) celled stages of the embryo-sac are 
formed in the usual manner. The sac increases in size very 
slowly up to this time, and the nuclei of the sac are of practically 
the same size (Figs. 6 and 7), except that antipodals are slightly 
smaller than the other nuclei. 
After the formation of the megaspore the ovule begins to 
enlarge, and a very pronounced growth of the nucellus and integu- 
ments on the micropolar side projects from the micropyle. The 
embryo-sac is thus left deeply imbedded in the nucellus (Figs. 4 
and 23). By the time the sac has reached the two-celled stage 
the nucellus shows two well-defined zones (Figs. 5 and 23). The 
inner zone surrounding the sac is made up of thin- walled cells, 
Contribution from the Botanical Laboratory of Ohio State University. XII. 
