THE FLOWER AND INSECT-POLLINATION 153 



and a much less frequent number is four. In the Mono- 

 cotyledons ( 87) with definite numbers, the prevailing num- 



FIG. 123. Dogtooth violet (lily family), with parts of the perianth all alike, and 

 hypogynous flowers. 



ber is three. This fact is a convenience in recognizing these 

 two groups without being compelled to examine the embryo. 



