LECT. X.] LEAVES THE PETIOLE. 517 



primary petiole springs from the branch, particu- 

 larly in those plants which have irritable leaves, as 

 Mimosa sensitiva, &c. At these secondary arti- 

 culations the leaflets separate, and fall in autumn; 

 sometimes before the common petiole falls, par- 

 ticularly when it is not articulated near its in- 

 sertion. The term inarticulatus is employed com- 

 paratively, when leaves belonging to a tribe of 

 plants, in which articulation is common, are de- 

 ficient in this peculiarity. 



The composition of the petiole necessarily im- 

 plies that of the leaf; but a compound leaf does 

 not necessarily imply the existence of either se- 

 condary, ternary, or partial petioles. The COM- 

 POUND leaf may be thus defined: a leaf which 

 consists of seveal distinct expansions or leaflets, 

 connected by articulations either directly or in- 

 directly, and a common footstalk. This defini- 

 tion differs from that of the majority of Botanical 

 writers, in regarding the connexion of the leaflets 

 by articulations as the chief charasteristic of the 

 compound leaf * ; but I cannot consider any leaf 



* Mr. Keith seems to be fully aware of this characteristic of 

 compound leaves (see Syst. of Phys. Bot. vol. i. p. 54) ; and 

 Bulliard thus defines the compound leaf: " La feuille composee 

 " a une ou plusieurs folioles attachees au petiole commun par 

 " une articulation, au moyen delaquelle chacune d'elles peut se 

 " mouvoir dans certaines circonstances, et 6tre detachee sans 

 " lesion, soit spontanement, soit artificiellement." Diet, ele- 

 ment, de Bolanique, p. 59. 



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