92 THE LEAF. 



(which is usually supported on a distinct stalk), is articulated 

 (articula, a joint), Avitli the main petiole, and separates from it 

 in decay. 



240. From the feather veined arrangement may result the 

 following forms of compound leaves : 



1. Pinnate (winged), where the petiole (midvein) bears a row 

 of leaflets on each side, generally equal in number and oppo- 

 site, as in the Acacia. 



2. A piimate leaf is said to be equally pinnate where the 

 petiole is terminated by neither leaflet nor tendril, as the Cassia 

 Marilandica, and unequally pinnate when it is terminated by an 

 odd leaflet or by a tendril. Ex. rose, locust, pea. In the latter 

 case the leaf is called cirrhose. 



3. An interruptedly pinnate leaf has the leaflets alternately 

 small and large, as in the potato, avens. 



4. A pinnate leaf sometimes consists of as many as twenty or 

 thirty pairs of leaflets, as in the Astragalus. Sometimes the 

 number of leaflets is but tlnee, and the leaf becomes ternate or 

 trifoliate, as in the ash ; and, finally, it is sometimes, by the non- 

 development of the pinna (pairs) reduced to a single terminal 

 leaflet, as in the lemon. Such a leaf is known to be compound 

 by the articulation of the leaflet to the petiole. 



5. A hipinnatc leaf (twice pinnate), is formed when the leaf- 

 lets of a pinnate leaf themselves become piimate. Ex. Fuma- 

 ria ofiicinalis. 



6. A tripinnate leaf (tluice pinnate), is formed when the leaf- 

 lets of a bipinnate leaf become pinnate, Ex. Aralia spinosa. In 

 the leaf of the honey-locust (Gleditschia), we sometimes find all 

 these three degrees of division, namely, the pinnate, bipinnate, 

 and tripinnate, curiously combined, illustrating the gradual tran- 

 sition of the simple to the most compound leaf 



7. A biternate leaf is formed when the leaflets of the ternate 

 leaf become themselves ternate, as in Fumaria lutea. 



8. A triternate leaf is formed when the leaflets of a biternate 

 leaf become again ternate. Ex. Aquilegia. 



241. The following forms of compound leaves may result 

 from the division of a radiate-veined leaf; the ternate, biternate, 

 &c., already mentioned ; 



