AMERICAN 
JOURNAL OF BOTANY 
Vol. 9 May, 1922 No. 5 
POTATO OVULES WITH TWO EMBRYO SACS 
W. J. Young 
(Received for publication July i, 192 1) 
Polyembryony, or the presence of two or more embryos in the seed, is of 
sufficiently uncommon occurrence to excite the interest of botanists when- 
ever found. In some few species it appears as the normal method of seed 
formation and is found quite regularly, as in the mango and in some of the 
Citrus fruits. In some varieties of the plum, peach, and other stone fruits, 
two kernels are often produced in the same pit. This is not true poly- 
embryony, but represents rather two seeds, derived from independent 
ovules, in the same indehiscent carpel. From the ecological standpoint, 
however, the two cases are equivalent, as there is no opportunity for the 
seeds thus formed to become separated in planting. 
True polyembryony may arise either by the development of embryos 
from two distinct eggs contained in separate embryo sacs in the same ovule; 
or one embryo may arise from the fertilized egg, the others being formed by 
some vegetative method, being developed from synergids or antipodal cells 
or formed by the budding of cells lining the embryo sac. The latter method 
is characteristic of the mango and Citrus fruits already cited. In the former 
case all embryos show the usual hereditary phenomena of sexual reproduc- 
tion; in the latter case such phenomena are shown only by the embryo 
developed as a result of fertilization. The other embryos transmit the 
characters of the ovulate parent as perfectly' as in any other method of 
vegetative propagation. 
It is not always possible to determine on examination of the mature seed 
by which method the embryos have been formed. In case the tissues of the 
nucellus persist as a perisperm, embryos produced in separate embryo sacs 
might be separated by a more or less definite layer of tissue. Embryos 
produced in the same embryo sac as a rule lie in direct contact, though 
even in this case there is a possibility of separation by a layer of endosperm. 
It is thus evident that the determination of the method of origin of the 
embryos from the anatomy of the seed is often difficult or impossible. 
The presence of more than one embryo sac in the ovule is not rare in 
some of the lower members of the Archichlamydeae, though the condition 
is very unusual in the Sympetalae and in monocotyledons. It is conse- 
quently worth while to record a case which came to the writer's notice in 
the Irish potato, Solanum tuberosum L. In the early development of the 
[The Journal for April (9: 159-212) was issued May 15, 1922] 
213 
