June, 1923] 
YOUNG-GERM CELLS IN THE POTATO 
331 
division of the original archesporial cell, though it is apparent that this 
is not the ordinary method of megaspore formation. It is very rare for 
the ovule to contain more than one mature embryo sac, yet three instances 
were found of what might be termed “double ovules.” 1 In each of these 
cases, two embryo sacs were found enclosed by the integument at some 
distance from each other. Such a condition would arise only when the ovule 
is abnormal from an early stage in its development, having two distinct 
growing points with the archesporial cells separated by a considerable 
extent of nucellar tissue. Archesporial cells lying side by side would 
normally develop embryo sacs lying in close contact in the ovule. 
The resting stage of the megaspore continues until about the time that 
the integument reaches the end of the nucellus and the pollen mother 
cells undergo the tetrad division. The megaspore, which has previously 
been somewhat angular, now elongates, its cell wall disappears, and its 
nucleus is somewhat enlarged. This is the one-nucleate stage of the embryo 
sac (PI. XXVI, fig. 1). The nucleus then divides (PI. XXVI, fig. 2), giving 
rise to the two-nucleate stage, one nucleus lying at each end of the embryo 
sac (PI. XXVI, Fig. 3). Owing to the lack of cell-division stages in the ovules 
in the material examined, it was not possible to determine at what stage 
chromosome reduction takes place, though the chromosome number was 
found reduced at the first nuclear division in the embryo sac. Two more 
nuclear divisions now follow in quite rapid succession, giving rise to the 
four- and eight-nucleate stages of the embryo sac. Meanwhile the embryo 
sac has increased considerably in size and become deeply buried by the 
integument. The contents have become vacuolated, and four nuclei are 
present at each end of the sac. 
The egg apparatus is now organized from the nuclei which lie in the end 
of the embryo sac nearest the micropyle (PI. XXVI, fig. 6). Two of these 
nuclei, with the surrounding protoplasm, form the synergids. These are 
rather small, pear-shaped cells which develop acute points fitting into 
the end of the embryo sac close to the micropyle. The protoplasm in the 
basal portion of the synergids becomes very dense and stains deeply, so 
that the small nuclei can scarcely be seen. The upper part of each synergid 
is occupied by a single large vacuole and protrudes into the cavity of the 
embryo sac. The egg is placed laterally to the synergids and extends 
much farther into the embryo sac. It consists of a relatively large nucleus 
surrounded by dense protoplasm and has a large basal vacuole. Like the 
synergids, it is attached in the micropylar end of the embryo sac. The 
fourth or polar nucleus withdraws somewhat toward the center of the 
embryo sac, where it is joined by a second polar nucleus from the opposite 
end of the sac. These nuclei lie close together for a time but finally fuse to 
form the primary endosperm nucleus. Though the polar nuclei are scarcely 
as large as the egg nucleus, they are more clearly visible owing to the lesser 
1 Amsr. Jour. Bot. 9: 213-214. 1922. 
