_ THE PISTIL 463 
structure of the Angiosperms, had to be introduced. That the 
ovary gives the Angiosperms a special economic importance is 
attested by the fact that our fruits are either ripened ovaries or 
ripened ovaries plus closely related parts. Within the ovary 
occur the cavities or locules in which are borne the megasporangia 
or ovules, varying in number and also in the way they are at- 
tached in different Angiosperms. 
The ovule is generally borne on a stalk (funiculus), and the 
chief structure of the ovule is the nucellus, which in most Angio- 
sperms is enclosed by two integuments, an inner and an outer one. 
As in Gymnosperms, the integuments do not completely close 
over the top of the nucellus, but leave a small opening (micropyle). 
Usually the ovule curves as it develops and the micropyle is 
brought around to near the base of the ovule. This position of 
the micropyle is a favorable one for the entrance of the pollen 
tube. There are terms used to indicate the amount of curving 
ovules undergo in their development. Ovules that remain 
straight are orthotropous. Those that double clear back upon 
themselves are anatropous. Those turning only part way back 
upon themselves are campylotropous. Within the nucellus is 
formed the megaspore mother cell (B, Fig. 408), which also 
divides by two successive divisions in one of which the number of 
chromosomes is reduced to the gametophytic number. A mega- 
spore, therefore, produces four megaspores, each of which is com- 
parable to a pollen grain. Although the megaspores are formed 
while the flowers are mere buds, they are formed later than the 
pollen grains. As in the Gymnosperms, in most Angiosperms 
only one of the megaspores develops into a gametophyte, although 
among Monocotyledons, there are cases in which more than one 
or all of the megaspores apparently take part in forming the one 
gametophyte. The lower diagram in Figure 409 gives the usual 
history of the megaspores. 
The female gametophyte is very much reduced, consisting of 
only a few nuclei and naked cells in a small mass of cytoplasm. 
In most Angiosperms the female gametophyte is developed in 
the following way. The megaspore first enlarges by digesting 
and using the other three megaspores and the adjoining cells of 
the nucellus as food. Then as the megaspore further enlarges 
the nucleus divides, and the daughter nuclei pass to opposite 
ends of the embryo sac which is the term now applied to the 
