RUTACE^ 



477 



Key to Important Genera of Rutace^"^ 



Leaves trifoliate, Ponciriis (trifoliate orange). 

 Leaves unifoliate. 



Ovary three- to seven-celled; ovules two in each cell; stigma cavernous, 



Fortunella (kumquat). 

 Ovary eight- to fifteen-celled; usually more than two ovules in each cell; 

 stigma solid, Cilrics (orange, lemon, grapefruit, lime, etc.). 



Fig. 201. — Sour orange (Citrus aurantium). A, flowering branch; B. 

 lengthwise section of flower; C, lengthwise section of fruit; D, seed. (After 

 Wossidlo.) 



CITRUS (Citron, Lemon, Orange, etc.) 

 Habit, Roots. — Citrus species are aromatic, mostly thorny 

 shrubs or small trees with the spines disposed singly in the 

 leaf axils. The sweet orange tree is a surface feeder; almost 

 its entire root system is in the first i8 inches of soil. The 

 sour orange root system penetrates to a much greater depth. 

 The citrus plant is different from most plants in the total 

 absence of root hairs. Absorption is carried on by the fibrous 

 roots which are abundant and capable of rapid growth. 

 Leaves. — The leaves are glandular-dotted, winged-petio- 



^Hume has been followed largely in the discussion of this group. 



