90 THE LEAF. 



26 Acerose (needle-shaped), when there is httle or no distinc- 

 tion of lamina, petiole, or veins, as in the leaves of the pine. 



§5. MARGIN. 



235. The margin of the leaf is also modified chiefly by the 

 same causes which affect the form. It is said to be 



1. Entire, when even-edged. This may result from the full development of the 

 tissue, or from a vein running parallel with the margin. Ex. lilac, lily. 



2. Dentate (toothed), the tissue incomplete, having teeth with concave edges, 

 pointing outAvards from the centre. Ex. hawkweed. If the teeth are very fine, 

 the margin is said to be denticulate. If the teeth are themselves toothed, it is 

 dovbly dentate. 



3. Serrate, having shai-p teeth pointing forward like the teeth of a saw Ex 

 Rosa. If the serratures are very small, it is serrulate. If they are themselves 

 serrate, it is doubly serrate. 



4. Crenate, notched with rounded or convex teeth, as in Glechoma. If such 

 notches are very small, it is crenulate. 



5. Erase (gnawed), having the margin irregularly toothed, or jagged, as if 

 bitten by animals. 



6. Undulate (wavy), the margin rising and falling like waves. Ex. Amaranthus. 



7. Spinous, when the veins project far beyond the tissue in sharp spines, as in 

 the thistle. Such leaves are said to be armed, and the opposite corresponding 

 term is umajmed. 



8. Incised (cut), margin divided by deep incisions. 



9. Laciniate (torn), divided by deep and irregular gashes. 



10. Crisped, margin much expanded and curled by a superabundance of tissue, 

 as in the mallows. 



11. Repand, having the margin slightly concave between the projecting veins. 

 Ex. Solanum nigrum. 



§6. APEX. 



236. In regard to the termination of a leaf at its apex, it is 

 said to be 



1. Acute, when it ends with an acute angle. 



2. Obtuse, when it ends with a segment of a circle. 



3. Acuminate, ending with a long, tapering point. 



4. Emarginate, having a small notch at the end. 



5. Retuse, terminating with a round end, having the centre depressed. 



6. Mucronate, abruptly terminated by a short, hard, bristly point, &c. 



§7. SURFACE. 



237. The following terms are employed in descriptive botany, 

 chiefly to denote the modifications of the surface (epidermis) 



