230 A TEXT-BOOK OF BOTANY 



sperms, called Monocotyledons and Dicotyledons, are char- 

 acterized by them, the former having the parts of the 

 flower in threes, the latter in fives. This does not mean 

 that all flowers of these two divisions have one or the other 

 number, but that these are the prevailing numbers in case 

 there is a definite number at all. Not a few Dicotyledons 

 have flowers with the parts in threes, and a still larger 

 number have them in fours. 



137. Staminate and pistillate flowers. In many cases 

 stamens and pistils are not found together in the same 

 flower. In such cases there are staminate flowers, that is, 

 those without pistils; and pistillate flowers, that is, those 

 without stamens. These two kinds of flowers may be 

 borne upon the same plant, which is then said to be 

 monoecious ' (one household) ; or upon different plants, 

 which are then said to be dioecious (two households) . These 

 terms are applied indifferently to the plants or to the 

 flowers, either the plants or the flowers being spoken of as 

 monoecious or dioecious. In a dioecious plant, therefore, 



FIG. 218. Hypogynous flower of Potentilla (A), and epigynous flower of apple 

 (B). After ENGLER and FRANTIC 



one can speak of staminate and pistillate plants, one bear- 

 ing fruit and seed and the other not. Many of our common 

 trees, as willows and poplars, are dioecious; and many more, 

 as oaks, walnuts, and hickories, are monoecious. 



