514 CONSERVATIVE ORGANS. [LECT. X. 



aspect and functions of a leaf, in leaves which 

 suffer that change which is termed alienated 

 (alienatum) ; that is, when the compound leaves 

 which are the first leaves of the plant, and na- 

 tural to the tribe, afterwards give place to 

 simple leaves, which are merely dilated petioles ; 

 as exemplified in several of the Mimosas from 

 Botany Bay. De Candolle has named these in- 

 termediate forms phyllodia. The transition might 

 be supposed to depend on the energy of the 

 plant diminishing with its growth; for, when a 

 plant of this kind is topped, the new leaves which 

 are put forth display the same characters as the 

 original foliage * ; but, that this is not the case is 

 evident, from the transition occurring constantly 

 in New Holland, where the genus has every op- 

 portunity of following its natural habits. The ma- 

 jority of petioles are slightly furrowed on the up- 

 per side ; but, when this is deep, it is particularly 

 denoted by the term channelled (canaliculatus), 

 and when much dilated the petiole is said to be 

 concave (concavus). In the last-mentioned in- 

 stance it sometimes partially embraces the stem 



* I saw an illustration of this fact yesterday (25th September 

 1821), in the garden of Comtesse de Vandes, near Bayswater. 

 An old plant of Acacia falcata, on which no pinnated leaves 

 had been seen for several years, had been cut down and had 

 put forth pinnated leaves, resembling in every respect, except 

 in size, the first leaves of the plant. The second series of shoots, 

 however, displayed falcated leaves only without any pinnae. 



