THE LEAVES OF VASCULAR PLANTS. 243 



lateral, instead of one being superior and the other 

 inferior. There are some species which, during the 

 whole of their lives, bear a mixture of petioles furnished 

 with the ordinary leaflets, and of petioles transformed 

 into Phyllodia; such are Acacia heterophylla, (PI. 6, 

 figs. 2, 3, 4, 5,) A. Sophorce, &c. Some bear upon their 

 superior edge one or two glands, wliich indicate the 

 place where the ramifications bearing the leaflets ought 

 to take their origin. All these characters show their 

 petiolary nature ; but the fibres of these petioles are 

 sufficiently separated to admit a small quantity of 

 parenchyma, and to bear stomata ; whence it results 

 that these organs perform physiologically the function 

 of a limb. Some analogous transformations take place 

 in some species of Oxalis, as O. Bupleiirifolia and 

 O. fruticosa. 



Thai which we have clearly seen to take place in follow- 

 ing the history oi Acacia heterophylla I presume does 

 so equally in some other less evident cases. Thus, for 

 example, the leaves of several species of Bupleurum 

 appear to me to be true Phyllodia ; they, in fact, com- 

 pletely resemble those of the Acacias, and are particu- 

 larly analogous to them, both in their hard extremity, 

 which denotes an abortion, and by their vertical position, 

 which is hardly ever met with in the true limbs of 

 leaves. These reasons are corroborated by the example 

 of Bupleurum difforme; this name has been given to the 

 only species which reveals the structure of the leaves of 

 this singular genus. In its young state it has, like the 

 A-cacias, leaves Avith the limb developed, and cut out in 

 the manner of the Umbelliferas : when full-grown it 

 has only Phyllodia. It is also to this or the preceding 

 class that I am inclined to refer the leaves of Ranun- 

 culus gramineus, and those of all Dicotyledons which 

 seem provided with longitudinal and parallel nerves. 



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