394 BOTANY OF CROP PLANTS 



two ovules; one of them aborts, the other develops into a 

 seed. The endosperm is absent, or present only in a small 

 amount. The cotyledons are fleshy. 



The only genus of any importance is Frunus. It has the 

 characteristics of the family. 



PRUNUS 



This genus includes the plum, cherry, almond, peach and 

 apricot. These main groups may be distinguished by the 

 following key: 



Key to Main Groups of Genus Prunus 



Stone smooth. 



Flowers clustered; fruit glabrous. 



Fruit large, usually grooved, covered with a bloom; stalk short; stone 

 usually compressed, longer than broad; leaves convolute in the bud 

 (Fig. loi). Plums. 

 Fruit small, usually not grooved, not covered with a bloom; stalk long; 

 stone usually globular; leaves conduplicate in the bud (Fig. loi), 

 Cherries. 

 Flowers solitary or in two's; fruit velvety at first, Apricots. 

 Stone pitted or furrowed. 



Flesh soft, thick, juicy, Peaches. 

 Flesh hard, thin, dry, Almonds. 



The genus has about 90 species, nearly all of which occur 

 north of the equator; they are widely distributed in both 

 eastern and western hemispheres. Most species are con- 

 fined to the temperate zone. The evergreen cherries include 

 a group found in the tropics and subtropics. 



PLUMS 



Stems. — The plums are shrubs or small trees. The 

 different species vary considerably in bark and twig charac- 

 ters. The bark of southern forms is lighter in color than 

 that of those growing in the north. Plums have a tendency 



