FOLIAGE AND SCALE LEAVES. 61 
ordinary form (Fraxinus excelsior) has well-marked pinnate leaves, 
but in an allied species (Fraxinus heterophylla) 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, &c. Thus we 
have bipinnate (fig. 12), tripinnate, &c., leaves. Palmate examples 
when thus compounded are usually of ternate type (fig. 25), 7.e., 
with successive trifurcations, and may be Diternate, triternate, &c. 
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 
arule. 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, 
