THE STEUCTUEE OF PLANTS. 



7 



longed portions oi lobes, instead of being round, are sharp and pointing 

 downwards, the leaf is arrow-shaped or sagittate (Fig. 182 and 243) ; or 

 if the lobes, instead of pointing downwards, are turned outwards, it is 

 halhert-shaped or hastate (Fig. 181) : if the lobes are rounded, it is auricu- 

 late or eared. "When the lobes of a kidney-shaped leaf unite, and the 

 petiole appears to be fixed in its centre, it is called peltate or shield- 

 shaped. 



24. Various terms are used to describe the apex or termination of 

 leaves and similar bodies, viz. : acute, when terminating in a sharp angle 

 without much tapering ; acuminate or pointed, if the apex is narrowed 

 into a point ; mucronate, if furnished with a small abrupt point ; obtuse, 

 if ending in a rounded blunt point ; truncate, when it appears as if cut 

 off abruptly ; rctuse, if slightly indented at the apex ; notched or emargi- 

 nate, when 'decidedly indented ; and ohcordate, when so much so as to be 

 reverse heart-shaped. 



25. The margin of the leaf, when without any notches or indentations 

 of any kind, is entire ; when with sharp teeth pointing forwards, like the 

 teeth of a saw, it is serrate. If the teeth point outwards instead of to- 

 wards the apex, it is said to be dentate or toothed; if the teeth are 

 rounded, it is crenate or scalloped. If these indentations of the margin are 

 small in degree, then the diminutives, serrulate, denticulate and crenulate, 

 are employed. 



A margin with a wavy outline is called repand, or if the indentations 

 are deeper, shallow and rounded, sinuate. When the teeth are irregular 

 and sharp, the leaf is said to be incised or cut. A lobed leaf has the mar- 

 gin deeply cut with a definite number of divisions ; if the divisions reach 

 nearly to the middle, it is cleft ; if nearly to the midrib, parted ; or it 

 quite to the midrib or base, divided. The number of these divisions is 

 expressed by numerals ; thus we say 2-lobed, 3-cleft, A-parted, &c. The 

 division of the margin follows the distribution of the veins, and a piu- 

 nately-veined leaf will he pinnatehj-cleft, pinnately-parted, &c., and a pal- 

 mately-veined one will be palmately-lobed, palmately-divided, &c. 



26. Leaves, as to the division of their margins, present every variety 

 from entire to so deeply cut that the division reaches the midrib. The 

 parts of a divided or parted leaf are called Segments or Lobes. However 

 much it may be divided, the leaf is considered as simple unless the parts 

 are jointed together, or articulated, in which case it becomes compound. 

 The parts of a compound leaf are called Leaflets, and the same terms are 

 used for them that are employed in describing leaves. Compound leaves, 

 like divided ones, present two principal forms : when a pinnately-veined 

 leaf becomes compound, it forms a pinnate leaf (Fig. 78), the leaflets 

 being arranged on the midrib which becomes the Common Petiole or 

 Rachis ; so a palmately or radiately-veined leaf becomes palmately com- 

 pound or digitate, bearing the leaflets at the top of a common petiole 

 (Fig. 64) . When the leaflets of a pinnate leaf are in even pairs, the 

 leaf is equally- or abruptly-pinnate ; odd-pinnate, if the common petiole 

 terminates with a leaflet (Fig. 53). Sometimes the common petiole is 

 prolonged into a Tendril (Fig. 71), and the leaf aids in supporting the 



