BOTANY OF CITRUS FRUITS. 13 



origin in southeastern Asia, though two are native of Aus- 

 tralia. From their native regions they have been carried 

 into all countries where the climate is suited to their 

 growth and into many others where artificial heat is 

 necessary for their welfare. 



Considerable difficulty has been encountered in 

 straightening out the botanical nomenclature of the species 

 and something still remains to be desired. For instance, 

 in 1813 (Ann. Mus. Par.) Risso described a species of 

 citrus, C. Limetta, which included the sweet limes, Adam's 

 apple, and a few others, but was not apparently intended 

 to include our acid limes. Under C. Limonum, he in- 

 cluded the sweet lemons and acid lemons and limes. In 

 1832, Roxburgh (Flor. Ind.) proposed the species C. 

 Acida to comprehend, as he said, "the sour lemons or 

 limes found in India, 7 ' but under it he describes (page 

 392, vol. 3.) one variety of sweet lime. His species may 

 be considered identical with Risso's C. Limonum. Hooker 

 in his Flora of British India, 1875, described the acid 

 limes, under the name C. Medica, Var. Acida. In the fol- 

 lowing classification, however, C. Limetta is applied to the 

 acid limes, which may be somewhat stretching the original 

 intent and purpose of Risso, while C. Limouum includes 

 only the acid lemons. 



Risso referred to the oil cells in the rind of citrus 

 fruits as being either concave or convex. Just what he 

 meant by this is not clear. It may be he referred to their 

 actual shape, or on the other hand it may be he had in 

 mind the form of the ends of the cells, where they touch 

 the outer plane of the rind. 



But in either case the concavity or convexity of the 

 oil cells as a basis of separation of the different species 

 and varieties appears to be worthless. Both kinds have fre- 



