CHAP. II. 
LEAVES. 
115 
lobes are themselves lobed, we may say tripennatisected, tri- 
pennatiparted^ &c. Finally, in cases where leaves are extremely 
divided, and the parenchyma of the ultimate ramifications of 
the veins does not unite and form lobes, we say, in general 
terms, that the leaf is multifid^ laciiiiated, decomposed, or slashed ; 
terms which express the appearance of a leaf, without any 
very precise signification." 
With regard to compound leaves, their leaflets always 
have the primary veins running at an angle more or less 
acute towards the margin. " This is perfectly intelligible if 
we reflect that their lateral veins represent not the primary, 
but the secondary and tertiary veins of simple leaves, which 
latter are always pennated. 
" The leaflets of pennated leaves are usually placed opposite 
each other in pairs along a common petiole. These pairs of 
leaves are called in Latin juga : thus a leaf with one pair is 
unijugum; with two pairs, bijugum, &c. 
" Usually one of the leaflets terminates the petiole ; the 
leaf is then unequally pinnated (imparipinnatum) ; but sometimes 
there is no odd leaflet, and the petiole ends abruptly, or in a 
point or tendril ; (this is equally pinnated, pari-pinnatum), 
" Sometimes the leaflets themselves are subdivided into 
other leaflets (folium bipinnatum, tripinnatum). In this case, 
the lateral petioles which bear the leaflets are called partial ; 
and the small supports of the leaflets themselves, stalklets 
(petiolules),** 
Such are De Candolle's ideas of the typical formation of 
leaves. They offer a convenient mode of studying the modi- 
fications in structure of these organs, and are, to all ap- 
pearance, founded upon a 
correct idea of the subject. 
The PETIOLE, or leafstalk 
{Jig. 56. a—b), is the part 
which connects the blade 
with the stem, of which it 
was considered by Linnaeus 
as a part. It consists of one 
or more bundles of fibro- 
vascular tissue surrounded 
I 
