478 BOTANY OF CROP PLANTS 



late, glaucous, leathery, evergreen, and unifoliate (with the 

 exception of Citrus trifoliate) ; the leaf stalk is usually articu- 

 lated to the blade and also to the twig. The life of the leaf 

 depends upon the kind of wood upon which it is borne. On 

 the fruiting branches, orange leaves, for example, remain on 

 the tree about fifteen months, while on twigs with vigorous 

 vegetative growth they may remain on the tree for three or 

 four years. The leaves of trifoliate oranges fall in the 

 autumn. The aromatic odor of freshly crushed leaves of 

 citrus plants is due to the numerous glands which are 

 scattered over its surface. 



Flowers.' — The white or purpHsh-pink flowers are solitary, 

 or in small axillary or terminal cjnnes or panicles. The 

 flowers are hermaphroditic; the calyx is three- to six- toothed; 

 the corolla has four to eight separate thick segments (petals) ; 

 and there are 20 to 60 stamens, united at their bases to form 

 groups; the ovary possesses 8 to 75 cells and is subtended by 

 a cushion-shaped disk (receptacle). 



Pollination and Fertilization. — Some varieties of citrus 

 plants require fertilization in order to set fruit, while 

 others mature parthenocarpic ("seedless") fruits. Some 

 varieties of oranges require cross-fertiHzation, and more- 

 over, will not set fruit unless pollen is derived from certain 

 congenial varieties. Pollination may occur without the 

 visitation of insects. The time for complete fertihzation 

 after pollination varies from thirty hours in Satsuma oranges 

 to four weeks in trifoliate oranges. Parthenocarpic varieties 

 seldom bear viable pollen. In navel oranges there is no 

 pollen in the anthers at flowering time. 



Fruit. — The fruit is a modified berry (hesperidium) ; 

 it is spherical or spheroidal and is made up of a thick, 

 leathery "rind" with numerous lysigenous oil glands, and a 

 juicy pulp composed of numerous stalked "juice sacks." 



