STRUCTURAL BOTANT. 51 



other two on the prolonged common petiole, while the 

 palmate has its three leaflets either sessile, or stalked alike. 

 (PI. II, 7.) 



103. Leaves EEPEATteDLY compound are those pinnate 

 or palmate leaves, in which the common petiole bears, in- 

 stead of leaflets, secondary petioles, supporting more than 

 one leaflet, which may have tertiary petioles, bearing a 

 number of leaflets in their turn. When the common 

 petiole of a leaf of the pinnate sort bears, instead of leaflets, 

 petioles furnished with two or more (sessile or stalked) 

 leaflets, the leaf is twioe-pinnate, or hipinnate (PI. II., 13) ; 

 and when the common petiole of a leaf of the palmate 

 sort gives off three petioles, each of them bearing three 

 leaflets, the leaf is twice-ternate or hitemate. (PI. II., 12.) 



If the division goes one step farther in this direction, a 

 leaf becomes thrice-pinnate or tripinnate (PI. II., 145), or 

 ihnce-temate (triternate) — PI. II., 14a. 



"When a compound leaf becomes more than thrice- 

 pinnate, or thrice-palmate, the leaf is said to be de- 

 compound. 



It happens, sometimes, that the secondary division be- 

 comes pinnate, although the primary one was digitate ; in 

 that case, we have the two sorts of compound leaves com- 

 bined in the same leaf. 



** MODIFIED LEAYES. 



103. Modified xeaves, whether extraordinarily 

 formed, or in any wise arrested in their development, 

 are those which are something else than foliage, as 

 pitGhersJiaped leaves {ascidia), fly-^aps (as in Dioncea), 

 scales, hracis, spathes, air-hladders (in some species of 

 TJtrioularia), tendrils (which, however, are sometimes 

 transformed branches), and spines. 



