'23 



of its own, there being no trace of lamina at the place of 

 insertion, and when each of them can he separated from the 

 common leaf -stalk without tearing, just as the whole leaf may 

 be separated from the stem, the leaf is known as a compound 

 leaf, in contra-distinction to a simple leaf which is not thus 

 divided. The parts of a simple leaf blade are known as Simple and 

 segments, or lobes, while each separate division of a com- Compound 

 pound leaf is called a leaflet. The terms given above for the 

 description of a simple leaf, as to its venation, margin and so on, 

 are equally applicable to each leaflet of a compound leaf. 

 Each leaflet may be sessile or provided with a stalk, the latter 

 being called a petiolule. The various shapes of the leaf blade 

 are. caused by portions of the leaf growing faster than others, 

 and we get first an uneven margin, then a lobed, cleft, parted, 

 and finally a divided, or compound leaf. As in such cases the 

 growth in the direction of the main nerves is usually more 

 vigorous than that of the portions of the blade between them, 

 a pinnately-nerved leaf gives rise to a pinnately-lobed, 

 cleft, parted, divided, or compound leaf, and a palmately- 

 nerved leaf to a palmately, lobed, cleft, parted, divided,, 

 or compound leaf. Pinnately- and palmately -cleft are synony- 

 mous with, and often replaced by, the terms pinnatifid and 

 palmatifid respectively 



Similarly the terms pinnately and palmately divided 

 are synonymous with the terms pinnatisect and palmatisect. 



23. The following terms are most General 



frequently employed for describing the general shape of the shape of 

 blade of a leaf or leaflet. They are of course applicable to Leaves - 

 any plane surface and so may be used for other organs 

 besides leaves. As they refer to plane surfaces with an 

 entire margin, in order to describe the general shape of a 

 leaf the margin of which is not entire, it is usual to con- 

 sider the general shape as defined by an imaginary line 

 passing through the base and apex of the leaf-blade and 

 touching the summits of all the principal teeth, lobes, or 

 segments, of the lamina. 



1. Acicular ; needle-shaped, very much longer than 



wide and tapering to a point, such as a Pine leaf. 



2. Linear ; several times longer than wide with almost 



parallel sides. 



3. Subulate ; awl-shaped, acicular with a broad base. 



4. Lanceolate ; like a spear-head. Several times longer 



than wide but tapering to both ends, with the 

 '. - greatest width below the centre. 



