ANGIOSPERMS 229 
(§ 123). On the outside of this ovule. one or two special 
coverings are developed, called integuments. These integu- 
ments grow up about the ovule, but do not completely 
cover it at the top, leaving a little opening called the 
micropyle (little gate). This micropyle is a very important 
A B Cc 
Fic. 217.—Diagrammatic longitudinal sections of ovules, snowing outer (07) and 
inner (iz) integuments, micropyle (m), nucellus (m), and megaspore (em), the 
last often called embryo sac: A, erect ovule; B, curved ovule; C, inverted ovule. 
feature in the ovule and also later in the seed. The body 
of the ovule within the integuments is called the nucellus, 
and within the nucellus the large spore (megaspore) lies 
embedded (Fig. 217). The three types of ovule are shown 
in Fig. 217: the erect ovule (A), the curved ovule (B), and 
the inverted ovule (C), the last being the most common. 
136. Floral numbers.—In many flowers there is no 
regularity in the number of members in each set. For 
example, in the water-lily petals and stamens occur in 
indefinite numbers; and in the buttercup the same is true of 
stamens and carpels. In most flowers, however, definite 
numbers appear either in some of the sets or in all of them. 
When these definite numbers are present, they are prevail- 
ingly either three or five; that is, there are either three or five 
sepals, petals, stamens, and carpels; although it is very 
common to have two sets of stamens, in which case they 
number six or ten. These numbers appear so constantly 
in great groups that the two grand divisions of Angio- 
