SECTION I 



LEAVES 



Leaves may be defined as appendages borne upon an axis but 

 differing from it in structure and organisation. They usually exhibit 

 three regions, viz. a leaf-base, a stalk or petiole, and a lamina or 

 blade. Each of these regions may offer characters that are useful 

 in identifying the leaf. The following schedule may assist the student 

 in examining leaves. 



i. Size and Shape. These may vary within certain, sometimes 

 rather wide, limits. Should the leaf have shrivelled so much as to 

 render them undeterminable it should be soaked in warm water and 

 gently spread out on a white tile. 



ii. Venation. The mode of branching of the midrib, the angle at 

 which the branches (lateral veins) leave it, the course they pursue, 

 and their elevation above or depression below the surface of the leaf 

 should be noted. 



iii. Margin. This margin may be entire, serrate, crenate, dentate, 

 sinuate, &c. 



iv. Apex. This may be rounded, pointed, notched, &c. 



v. Base. The appearance of the base should also be noted. 



vi. Surface. The surface should be examined with a lens, and 

 the presence or absence of hairs, as well as the character of the latter, 

 glandular or otherwise, determined ; this particular is of very great 

 importance. 



vii. Glands. Many leaves contain internal oil-glands or oil-cells 

 which can usually be seen as translucent points when the leaf is 

 examined with a lens by transmitted light. In very thick leaves 

 they may be difficult to see, and it may be necessary to examine a 

 section under the microscope. 



viii. Texture. Papery, leathery, fleshy, &c. 



ix. Colour. Greyish green, dark green, &c. 



x. Odour. This is best determined by crushing the leaf between 

 the fingers and smelling it. 



xi. Taste. Often very characteristic. 



xii. Petiole. Presence or absence, length, &c. 



