48 



LEAVES. 



divisions extend to the midrib or petiole ; this has the appear- 

 ance of a branch with separate leaves attached to it. The 

 whole is considered as one leaf, because in its earliest state it 

 arises from the axis of a single piece ; and its subsequent di- 

 visions in the form of leaflets, are all in one plane. 



a. Pinnate (from pinna, a wiiig) : Fig. 47, a, represents the petiole, or principal 

 leaf-stalk, bearing leaflets arranged opposite to each other ; these may be either 

 petioled or sessile ; h b represent the stipules ; the whole taken together forms 



one compomid pinnate leaf. Binate ; when two leaflets only spring from the 

 petiole, as in Fig. 47, c. Ternate; when three leaflets arise from the petiole, as 

 Fig. 48, a. Biternate is a second division of threes, as Fig. 48, 6. Triternate is a 

 third division of threes, as Fig. 48, c. Decompound, 

 when a pinnate leaf is again divided, or has its 

 leaves twice compound, as Fig. 49, a. At 6 is a 

 representation of tricompound leaves. 



56. Various apj^earcmces of Leaves. 

 ■ — Compound leaves are confined to 

 Exogenous plants, and are reticulated, 

 or net-veined. Parallel-veined leaves, 

 though divided, are never jointed ; 

 therefore, in Endogenous plants, there are no compound leaves. 



Fig. 50, at a, is a leaf of the Ilex aquifolium (holly) ; it is oval and dentate, with 

 ipinescent teeth. 



6 is a leaf of the Malva-crispa (mallows) ; it is seven-lobed, crisped, or irregularly 

 piatted, and finely crcmdate ; venation, radiate. 



c is a leaf of the Hydrocotyle tridcntata ; it is cuneiform, dentate at the summit. 



i^ is a leaf of the Corchorus japonicus ; it is oval-acuminate, doubly denticulate 



Fig. 50. 



Fig. 51, <x, is Bk flahelliform or fan-shaped leaf, two-lohed, and crenulate. 

 b is oval-acumijiate, Jive-ribbed, ribs converging, 

 c is sub-cordate, oval-acuminate, undulate. 



a. Pinnate— Binate— Ternate— Biternate— Triternate— Decompound,— 56. No compound leaves in 

 £^ndogenoas plants. — Explain figures 49, 50. 



