104 MORPHOLOGY OF LEAVES. 



except at the base, which is simply pinnule or with one or two 



pairs of simple leallcts. 



Tripinnate or Tlu-in- Pinnule leaves of a regular sort are rare ; 



but. wiili some irregularity, they occur in many species, as in 



Aralia. &c. This extent of division, and even much greater. i> 



forninon in Ferns. 



Diyitiiti'-l'liniatr is where the primary division of the petiole is 



on the palmate or digitate plan ; the secondary, on the pinnate. 



This seems to he the case in the Sensitive Plant. Mimosa pudica. 



Fig. 201*. Hut the leaf is here truly Inpinnate with the primary 



dm.sions very crowded at the apex of petiole. 



Conjugate- f innate is the same arrangement, with the primary 



divisions a single pair, at the apex of the petiole, and the leaflets 



pinnately arranged on these. 



Digitately or l'ulint>-ly Decompound in a nearly regular way 



is not an uncommon case. 

 Usually, the petiole is succes- 

 sively three-forked, as in Fig. 

 210, when the leaf is said to 

 le bltcnmt? (twice teniate). 

 triternate (thrice ternale). or 

 quadritemate (lour times ter- 

 nate), etc.. according to the 

 nuinher of times it divides, or 

 2-3 4:-timestemately compound. 

 The ultimate divisions in such 



cases of threes are commonly of the pinnately trifoliolate type. 



201. Finn* is a convenient name for the partial petioles of a 

 bipinuate leaf, taken together with the leaflets that belong to 

 them. Thus, the Sensitive Plant. Fig. 20'.). has four piniuv. or 

 two pairs; the Honey Locust, Fig. 208, a greater number. 

 When such leaves are still further compounded, the pinna' of 

 higher order, or the ultimate ones, take the diminutive term of 

 PINNTI..K or PINXTLES. The blades these beat- are the LealleN. 



202. The Petiole or Leafstalk is a comparatively unessential 

 part of the leaf. It is often wanting (then the blade is .sv.vsVA-) : 

 it may lie absent even in compound leaves of the palmate type, 

 the leaflets rising side by side from the stem. When present, it 

 is usually either round, or half-cylindrical and channelled on the 

 upper side. In the Aspen, it is flattened at right angles with 

 tin- blade, so that the slightest breath of air puts the leaves in 

 motion. Sometimes it is much dilated and nicmbranaeeous at 



KM!. 210. Quadri-teniivtely compound or ternately decompound leaf of Tbalictruin 

 Cornuti. 



