Morphology of the Citrus. 209 



The lima of Ceylon, or C. hystrix, has its first two 

 opposite leaves without joints, but the third leaf at 

 once shows the joint and margined petiole, the latter 

 becoming larger and larger as new leaves develop ; 

 see pis. from 246 to 255. 



There is, I think, some reason to suppose that the 

 original leaf of the citrus was a simple leaf. This idea 

 is strengthened by the enormous winged petiole of the 

 C. hystrix, and also by the typical emargination of the 

 distal end of the leaflets in all citrus, whether acuminate 

 or not. This indentation would appear to be the posi- 

 tion of another, though abortive, leaf expansion or 

 bud.* So that not impossibly the original leaf of the 

 citrus was only the winged petiole of to-day. Then by 

 another expansion or leaf bud from the petiole emar- 

 gination at the tip the leaflet originated, and by side 

 buds the trifoliate leaf was formed. One might, per- 

 haps, familiarise himself with this view by considering 

 how the branches of the Epiphyllum, one of the cac- 

 tacese, are formed. Fig./; pi. 245, gives a diagram of 

 it. The fully developed leaf of the C. hystrix, pi. 225, 

 figs, dfand e, would appear only a modification of some- 

 thing like an Epiphyllum branch. Then, if by pro- 

 liferation from the joint, which may be considered as a 

 node, a pair of additional bark expansions occurred, we 

 would get diagram fig. g, pi. 245, which would resemble 

 a part of the leaf of the Limonia, Feronia, and others. 

 In the leaf of the Limonia, pi. 245, a, b and c, there 

 would appear to be a tendency to this mode of pro- 

 liferation, carried on almost to any extent. f In such 

 case, the original trifoliate leaf of the citrus would have 



* Such as may have occurred in the leaf of the Limonia referred to. 



f The simple leaf being an expansion of the bark, the compound 

 leaf might, perhaps, be considered as a branch-form expansion of the 

 same. 



P 



