FORMS OF COMPOUND LEAVES. 



93 



pairs, multijugate (fig. 191). When a pinnate leaf ends in a pair of 

 pinnae (fig. 193) it is equally or abruptly pinnate (pari-pinnate) ; when 

 there is a single terminal leaflet (fig. 191), the leaf is unequally pinnate 

 (impari-pinnate) ; when the leaflets or pinnse are placed alternately on 

 either side of the midrib, and not directly opposite to each other, the 

 leaf is alternately pinnate (fig. 191) ; and when the pinnae are of dif- 

 ferent sizes, the leaf is interruptedly pinnate (fig. 196). 



In the case of a simple multicostate leaf with radiating venation, 

 if we suppose the ribs to be covered with parenchyma, so as to form 

 separate leaflets, each of which is articulated to the petiole, the digitate 

 form of compound leaf is produced ; if there are three leaflets, the form 



Fig. 196, 



Pig. 198. 



is ternate (figs. 156, 197); if four, quaternate (fig. 157); if five, quinate ; 

 if seven, septenate (fig. 192), and so on. If the three ribs of a ternate 

 leaf subdivide each into three primary veins, which become covered 

 with parenchyma so as to be separate articulated leaflets, the leaf is 

 hiteirnate ; and if another three-fold division takes place, it is triternate 

 (fig. 198). 



General summary of facts connected with the venation and con- 

 formation of leaves : — 



1. Leaves of flowering plants are either netted-veined (reticulated) or parallel- 



reined. 



2. Leaves have either a single midrih (nnioostate), or several ribs (multicostate); 



and the latter are either radiating (spreading out from one point), or con- 

 'vergent. 



3. Unicostate leaves have veins proceeding at different angles from various points 



of the midrib, and arranged more or less like the parts of a feather. 



Fig. 196. Imparl- alternately and interruptedly pinnate leaf. Leaflets or plniiEe sessile, 

 and serrated at the margin. Fig, 197. Ternate leaf of Strawberry. Margin of leaflets, 



toothed or dentate, p, Petiole with projecting hairs. I, Lamina divided into thi'ee 

 leaflets. Fig. 198. Triternate leaf. Leaflets cordate. 



