INTRODUCTION 
leaf consists of a blade, a stalk or petiole , and a sheath ; but either of these 
may be absent, and there may or may not be in addition two lateral lobes or 
appendages at the base, known as stipules. Thus in the Yellow Vetchling 
[Lathyrus Aphaca ) the blade of the leaves is replaced by a tendril, whilst its 
functions are performed by two large leafy stipules ; and in the related 
Crimson Grass Vetchling ( Lathyrus Nissolia) the blade is also absent, but 
there is a long vertically-flattened petiole, known as a phyllode, like the 
leaf of a grass. Leaves with petioles are termed petiolate ; those without, 
sessile (Latin sessi/is, sitting) ; those with stipules, stipulate ; those without, 
exstipulate. It is in but few cases that a sheath and stipules occur in the 
same leaf, as they do in the Rose. The various characters to be noted 
in describing leaves are their vernation , or folding in the bud ; their 
position and arrangement on the stem ; their insertion , i.e. the presence or 
absence of a petiole ; the stipules ; the venation or arrangement of the 
so-called veins ; whether they are simple , i.e. unbranched, even if deeply 
lobed, or compound , i.e. made up of distinctly articulated leaflets ; their 
outline , surface , texture , colour , and duration. 
In the bud the leaves of Oaks and Cherries are folded individually 
down their midribs, the two halves together, like those of a sheet of 
note-paper. This is termed conduplicate. The leaves of 
Beech and Sycamore are plicate, or folded like a fan, though 
the folds in the latter radiate with the principal veins or ribs of the leaves 
[palmately], whilst those of the former are parallel to the secondary 
transverse veins [pinnate ly) . Plums differ from their near allies the 
Cherries in having their leaves rolled up in the bud from side to side, like 
a scroll, or convolute : Violets, Water-lilies, and Butterworts have both 
margins rolled inwards or upwards, toward the upper surface, or involute ; 
whilst Heaths, Docks, and several sand-dune grasses have them rolled 
backwards toward the lower surface, or revolute. Collectively the young 
leaves in a bud may be valvate , when they touch without overlapping, 
like swing-doors ; imbricate , when they overlap like tiles on a roof ; or 
equitant , when, as in Iris, each leaf is conduplicate and its two edges 
overlap those of the next leaf in succession, as if astride of them. This 
Vernation 
xxm 
