158 
INTRODUCTION TO BOTANY 
The internal structure of seeds differs greatly in the vari- 
ous kinds. Some contain no separate parts that can be readily 
Fie. 140. Length- 
wise section of 
squash seed 
hi, hilum, or sear, 
marking place of 
attachment to the 
ovary; hyp, hypo- 
cotyl: p, plumule; 
c, cotyledon; e (in- 
nermost layer next 
to cotyledon), en- 
dosperm; ¢, testa. 
Two and one-half 
times natural size 
m the embryo itself (figs. 140 and 141), 
as in the chestnut, hazel, beech, oak, 
made out. Many kinds, however, consist of 
1. An embryo, or miniature plant. 
2. Some plant food stored elsewhere than in 
the embryo. This is usually called endosperm.? 
3. A seed coat or coats. 
Frequently the embryo is found to have a 
fairly well-defined set of organs: the hypocotyl, 
or little stem; the cotyledons, or seed leaves ; 
and the plumule, or seed bud. 
149. Classification according to number 
of cotyledons. The seeds of one great divi- 
sion of seed plants, the monocotyledons, com- 
prising grasses, sedges, palms, lilies, and 
many other groups, have one cotyledon. As 
shown in figure 158, 
B, the reserve food is 
stored mainly outside 
the embryo. 
The seeds of the 
other and still larger 
division, the divvtyle- 
dons, have two cotyle- 
dons (figs. 141 and 
144). The plant food 
in the seeds of dicoty- 
ledons is often stored 
Fie. 141. A common bean 
split open, after soaking 
in water 
h, hypocotyl, lying on one of 
the cotyledons; g, groove in 
the other cotyledon, where 
the hypocotyl] lay; p, plumule 
pea, bean, squash, and sunflower; or 
often between or around the cotyledons of the embryo, as 
in the buckwheat, four-o’clock, castor bean, honey locust, and 
morning-glory (fig. 144). 
1 Reserve food that was formed outside of the embryo sac is called 
perisperm. 
