POLYEMBRYONY 467 
from the embryos of Dicotyledons in the relative positions of the 
cotyledon and plumule. Although the cotyledon apparently 
arises laterally, it soon becomes terminal and the plumule appears 
to develop on the side of the em- 
bryo (Fig. 413). 
Parthenogenesis. — Partheno- 
genesis, which is the develop- 
ment of an embryo from a sup- 
posedly unfertilized egg, occurs 
in a number of Angiosperms. 
In the Dandelion (Taraxacum), 
Meadow Rue (Thalictrum), Ever- 
lasting (Antennaria), Apples, 
Pears, Quinces, and a few other 
plants parthenogenesis is known 
to occur. In cases which have 
been investigated cytologically, it 
has been found that the mother 
cell in the ovule omits the reduc- 
tion division, and, therefore, the 
cell which occupies the position of 
an egg has the sporophytic num- 
ber of chromosomes and fertiliza- 
tion is not necessary. Since par- Fic. 413. — A monocotyledon- 
thenogenetic plants show no re- 0US embryo as typified by that of 
: : : Corn. The cotyledon (c) appears 
sults of crossing in Ghee ON SPrING:  ccctial and the alumwmale (py a2 
when cross-pollinated, partheno- arising from the side of the em- 
genesis may be a source of disap-__ bryo. 
pointment to the plant breeder. 
Parthenocarpy. — Parthenocarpy is the development of fruit 
without fertilization and is quite common among Angiosperms. 
Bananas, seedless Oranges, and seedless Currants are familiar 
examples of parthenocarpic plants. Sometimes Apples develop 
without seeds, and some varieties of Cucumbers develop fruits 
without pollination. 
-Polyembryony. — In a few Angiosperms, of which one of the 
Onions (Allium) is a notable example, a number of embryos may 
be developed in the same embryo sac or around it. The syner- 
gids and antipodals have been known to develop embryos, and 
sometimes some of the cells of the nucellus around the embryo 
