ORGANS OF NUTRITION. 



159 



is very iiTegular and twisted and curled, as in the Garden 

 Endive, Cui-led Dock, and Curled Mint, it is said to be crisped 

 or curled {fiy. 303). 



2. Incision. — This term is used when the margin is more 

 deeply divided than in the above instances, so that the par- 

 enchyma does not usually extend more than about midway be- 

 tween it and the midrib, or petiole. The divisions are then 

 commonly called lobes, and the leaf is described as two-lobed, 

 three-lobed, four-lobed, &c., according to their number. It is 

 usual however to give different names to these lobes, according 

 to the depth of the incisions by which they are produced; thus 

 if they reach to midway between the margin and midrib, or 

 petiole, they are properly called divisions or lobes (Jig. 293), and 

 the intervals between them fissures, or in composition the term 

 -fid is used, and the leaf is said to be cleft; if nearly to the 

 base, or midrib {fig. 304), partitions, and the leaf is partite; if 

 quite down to the base, or midrib, segments (fig. 30.5), and the 

 leaf is dissected, or in composition -sected. These segments 

 differ from the leaflets of compound leaves in not being arti- 

 culated, and especially also in being united to the midrib, or 

 petiole by a broad base. 



In describing the above leaves we say that they are bifid or 

 two-cleft, trifid or three-cleft, quinquefid or five-cleft, septewfid or 

 seven-cleft, or multifid {many-cleft), according to the number of 

 their fissures. A leaf is also said to be tripartite, or trisected, 

 &c., in the same manner, according to the number of partitions 

 or segments. These terms are 

 especially used wdth palmately 

 veined leaves. 



The divisions of leaves are 

 always arranged in the direction 

 of the prominent veins. Thus 

 those of feather-veined or pin- 

 nately veined leaves are directed 

 towards the midrib; while those 

 of palmately or radiated veined 

 are arranged towards the base of 

 the leaf. Hence instead of using 

 terms indicating the number of 

 lobes, &c., of a leaf, others are 

 frequently employed that define 

 the leaf more accurately, and 

 which are derived from the mode 

 of venation combined with that 

 of division. Thus if the leaf is 

 feather-veined and the incisions 

 consequently arranged in that 

 manner, it is said to be pinnati- 



Fig. 304. 



Fig. 305. 



Fig.SOi. Leaf of the Valerian (Vale- 



riaiui dioica). F(sr.30o. Leaf of a 



species of Poppy (.FapaverArgemone). 



