68 THE LEAVES. [CHAP. 



unequally pinnate because there is an odd leaflet at the 

 end of the common petiole. When the odd leaflet is 

 absent the leaf is equally or abruptly pinnate. A leaf 

 becomes twice pinnate (pi-pinnate) when the common 

 petiole, instead of bearing leaflets, bears secondary 

 petioles upon which the leaflets are pinnately arranged. 



When leaflets are arranged on the digitate plan, and 

 are but 3 in number, they are called ternate, and the leaf 



FIG. 47. Digitate leaf of Horse Chestnut. 



is tri-foliolate, as in Clover and Strawberry ; if 5, quin- 

 ate, the leaf being quinque-foliolate. The leaflets may be 

 twice ternate (bi-ternate] if the petiole bears 3 secondary 

 petioles, each of which bears 3 leaflets, and so on. 



ii. The point of a leaf or leaflet at which the midrib 

 ends is called the apexj the point where it passes into 

 the petiole, or, if the leaf be sessile, where it is joined to 

 the stem, the base. The apex and base vary considerably 



