118 STRUCTURAL BOTANY. [100,101. 



elliptical, or even orbicular forms ; and if the lower 

 curve downward, the cordate, sagittate, etc. Palmate 

 forms there also are, splendidly developed in the Pal- 

 metto and other Palms, whose large leaves are appro- 

 priately called flabelliform (fan-shaped). 



299. The leaves of the Pine and the Fir tribe (Coni- 

 ferse) generally are parallel-veined also, and remark- 

 able for their contracted forms, in which there is no 

 distinction of petiole or blade. Such are the Acerose 

 (needle-shaped) leaves of the Pine, the Subulate (awl- 

 shaped) and scale-form leaves of the Cedars, etc. 



CHAPTER XXII. 



THE COMPOUND LEAF, ETC. 



300. If we conceive of a simple leaf becoming a 

 compound one, on the principle of " deficiency of tissue 

 between the veins," it will be evident that the same 

 forms of venation are represented by the branching 

 petioles of the latter as by the veins of the former. 

 The number and arrangement of the parts will there- 

 fore in like manner correspond with the mode of 

 venation. 



301. The divisions of a compound leaf are called 

 leaflets ; and the same distinction of outline, margin, 

 etc., occur in them as in simple leaves. The petiolules 

 of the leaflets may or may not be articulated to the 

 main petiole, or rachis, as it is called. 



302. Pinnately compound. From the pinnate-veined 

 arrangement we may have the pinnate leaf, where the 

 petiole (midvein) bears a row of leaflets on each side, 

 either sessile or petiolulate, generally equal in number 



