FOLIAGE AND SCALE LEAVES. 6 1 



ordinary form (Fraxinus excelsior) has well-marked pinnate leaves, 

 but in an allied species [Fraxinus heterqpkylla) others, reduced to 

 one leaflet, are found in addition. The remarks previously made 

 about the variations in size and shape of the lobes in simple 

 leaves apply with equal force to leaflets. Many leaves are much 

 divided or decompound, the primary leaflets being split up into 

 secondary, and these in some cases into tertiary, kc. Thus we 

 have bipinnate (fig. 12), triplnnate, &c, leaves. Palmate examples 

 when thus compounded are usually of temate type (fig. 25), i.e., 

 with successive trifurcations, and may be alternate, triternate, kc. 

 The lamina, like the petiole, may be absent, as in phyllodes, or 

 it may undergo special modifications. Many tendrils are leaf- 

 structures, and the best examples are found in the pinnate leaves 

 of peas, vetches, and the like. Compare in this respect the 

 common field vetch or tare, the edible pea, and the sweet pea. 

 The leaves of the first possess seven pairs of normal leaflets, but 

 one or more pairs at the end are transformed into tendrils, and 

 the axis also ends in a tendril. The leaf of the edible pea is 

 similar, but there are five tendrils, one being terminal, and only 

 two pairs of green leaflets. In the sweet pea there are an odd 

 and two to four pairs of tendrils, and only one pair of leaflets, as 

 a rule. Sometimes, however, a third leaflet occurs with a tendril 

 opposite to it, the nature of which is thus clearly proved. 



Protecting spines are often formed by the modification of the 

 lamina. Sometimes only part is thus modified, as in the holly, 

 but the transformation may be complete, as in gorse. Here we 

 get branch spines bearing leaf spines. The nature of the latter 

 may be well observed in seedlings, the early leaves of which 

 are ternate. In succeeding leaves the leaflets gradually become 

 narrower and more spiny. The barberry is another instructive 

 example, presenting, as it does, in the same shoot all gradations 

 between leaves with spiny edges and three to seven -branched 

 leaf spines. 



The leaf blades of insectivorous plants (cf. p. 54) are often 

 modified for the purpose of securing prey. In the round-leaved 

 sundew (Drosera rotundifolia), which is not uncommon in marshy 

 places, the flower-bearing stems rise from the centre of a rosette 

 of leaves, each of which possesses a short stalk and a rounded 

 blade, the upper side and margin of which bear a large number 

 of so called "tentacles." These are emergences, resembling 

 minute pins in shape, the heads being glandular. In fresh leaves 

 each gland is tipped by a drop of the viscid clear excretion, 

 the appearance of which has given rise to the popular name. 

 Venus' fly-trap is a plant closely related to the preceding, and is 

 found in North Carolina. The petiole is here broadly winged, 



