CHAPTER XVI 
THE SEED AND THE SEEDLING 
196. From Ovule to Seed. — At the time of fertilization, 
an ovule consists of a mass of tissue ( nucellus ) in which is em¬ 
bedded the embryo sac. The embryo sac contains an egg 
cell which, if fertilized by a nucleus from the pollen tube, 
will become a young bean plant (embryo). The ovule is 
covered by two coats ( integuments ) which do not quite meet 
at one end, leaving an opening, the 
micropyle (ml'kro-pll: Greek, micro, 
small; pyle, gate), a small door 
through which the pollen tube usually 
enters. It is attached to the wall of 
the ovary (placenta, see § 184) by a 
stalk (funicle, see § 193) through 
which it gets its nourishment. 
In developing into a seed several 
changes occur. (1) The integuments 
become firm and hard, the outer 
forming the testa. (2) The egg cell 
divides, forming the embryo. (3) The embryo sac is replaced 
by two cotyledons (kot-y-le'don: Greek, kotyledon, socket) 
which contain food for the embryo. (4) The micropyle be¬ 
comes smaller and almost closes. (5) The funicle drops off, 
leaving a scar on the bean seed, the hilum (hl'lum: Latin, 
hilum, a little body). 
197. Adaptations of the Seed. — The bean seed is the plant's 
way of providing for a new bean plant. It is adapted to 
fulfill that purpose in the following ways. (1) A ripe seed 
219 
Figure 207. — Bean Seed 
Showing Parts. 
