.54 PART I. THE MORPHOLOGY OF PLANTS. [ 12. 



Occasionally the margin of the lamina bears outgrowths which 

 are not connected with branching, but are of the nature of emer- 

 gences, as in Mnium serratum, the Cherry Laurel, Naias, various 

 Conifers, etc. 



A number of terms are used in Descriptive Botany for the purpose of precisely 

 describing the various parts of plants. The more important of these terms, and 

 those the meaning of which is not obvious, will now be defined. 



(1) The Outline of bilateral bodies, such as the lamina of the leaf, but of 

 multilateral bodies, such as fruits, as well, is said to be linear when the two 

 margins run nearly parallel to each other ; e.g. the leaves of most Grasses. 

 If the margins are curved and intersect at each end at an angle, the outline 

 is said to be lanceolate or elliptical, accordingly as the long axis is many times 

 longer than, or only twice as long as, the transverse axis. If the two curved 

 margins round off at each end, then the terms oblong and oval are to be sub- 

 stituted for tbe two preceding. 



If the longest transverse diameter lies relatively near to the base, then the 

 outline is said to be ovate ; if relatively near to the apex, olovate. 



(2) The Apex may be either acute or obtuse ; when it is long drawn out it is 

 said to be acuminate ; when there is a sharp projecting point, it is said to be 

 mucronate (Fig. 32 F) ; truncate, when it is, as it were, cut short across (Fig. 

 32 D) ; emarginate, when there is a depression in the obtuse apex ; obcordate, 

 when the apical depression is deep. 



(3) The Base may be described by many of the preceding terms, but the 

 following are especially applied to it : it is cordate when it is deeply indented 

 in the median line ; sagittate, when the lobes on each side of the indentation are 

 angular and diverge backwards ; hastate, when the lobes diverge outwards. 



(4) The Margin is said to be entire when it does not present any depressions 

 or prominences ; when the prominences are slight and rounded, the margin is 

 said to be crenate ; dentate or toothed, when the prominences are pointed and 

 stand straight outwards ; serrate, when the pointed prominences slant for- 

 ward. 



If the incisions in the margin are deep, the part, a leaf-blade for instance, 

 or a gamosepalous calyx, is said to be lobed when the incisions do not extend 

 to the middle ; if they extend to the middle, it is said to be partite ; and 

 dissected when they extend nearly to the base (Fig. 32 (7). 



The segmentation of the lamina takes place in some Monocotyledons (Palms) 

 in an altogether different manner from that described above. The lamina is 

 at first entire, but it becomes divided by the dying away of strips of tissue (see 

 also p. 22). 



The Venation of tlie Lamina. The mid-rib and other ribs of the 

 lamina indicate the course of the larger vascular bundles; and 

 from thece, numerous branches are given off which permeate the 

 tissue of the lamina, constituting its Venation. When the leaf 

 decays, the ribs and the vascular tissue persist longer than the 

 soft parts as a skeleton which retains the general form of the lamina. 



