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 



em-, 



B 



FIG. 217. Diagrammatic longitudinal sections of ovules, showing outer (oi) and 

 inner (u) integuments, micropyle (TO), nucellus (n), 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- 



