54? THE LEAF. PART ! 



language of botanists, compound. The portion 

 from which the primary divisions proceed is called 

 the primary petiole; the divisions thus formed are 

 called the secondary petioles ; and the subdivisions of 

 these last are called the ternary petioles. Hence 

 the principal distinctions which botanists have in- 

 troduced into their descriptions of compound leaves. 

 If the petiole is itself undivided but supporting 

 several distinct expansions at the extremity as in the 

 Strawberry, the leaf is said to be digitate. (PL II. 

 Fig. 4.) If the leaflets or distinct expansions 

 are arranged on opposite sides of the petiole as in 

 the Pea and Vetch, the leaf is said to be winged. 

 (PL II. Fig. 5.) If the insertions of the leaflets 

 are opposite, the leaf is said to be oppositely 

 winged, and if they are alternate it is said to be al- 

 ternately winged. If the petiole supports an odd 

 leaflet at the extremity, the leaf is said to be 

 oddly winged ; if it does not support an odd leaflet 

 at the extremity it is said to be abruptly winged ; 

 and if the primary petiole is furnished with se- 

 condary petioles, which are again furnished with 

 leaflets, or with ternary petioles, it is then said to 

 be doubly or trebly winged as in the leaves of Fool's 

 Parsley and Common Hemlock. (PL II. Fig. 6.) 

 Figure of The figure of the leaf or expansion has been 

 ^ O e n expan ~ found to be of great use to botanists in the discrimi- 

 nating of the different species of a genus ; and the 

 consequence is, that they have spared no pains nor 

 labour to determine by observation and descriptioi 



