_ oo t => 
~ ' . ch e = eda = 
2 Cae i Pes t.9 \ : r Sy s- ‘ { Ak ee eA RS eee 
\ / i} we Ve P d . skeet Vln ” ¥ 
y a 
ie ’ 
94. ~~ Structural and Physiological Botany. a 
form. In the former case the two margins of the base of 
the leaf have united ; while the latter variety consists of 
two leaves which have become completely united at the 
base in their growth. Not unfrequently the leaf is united 
for a certain length with the stem, when it is said to be 
decurrent [and the stem to be wénged], (Figs. 151, 152). 
The Zamina or blade, the most essential part of the leaf, 
may assume almost any conceivable form. The first thing 
to observe is whether the petiole bears only a single lamina, 
or several, connected with it by secondary petioles or fetzo- 
Fic. 153.—Lanceolate leaf 
Fic. 152.—Decurrent spiny leaves of thistle, the stem 
of the privet. 
a hence becoming winged. 
Jules, or by articulations. In the first case the leaf is said to 
be stmple, in the latter cases compound. 
The separate leaflets of a compound leaf, as well as the 
single lamina ofa simple one, may have the greatest variety 
of external form. Zznzear leaves are such as are not only 
many times longer than broad, but are of nearly the same 
width from the base to near the apex, as in nearly all grasses. 
‘Tf the leaves are at the same time somewhat rigid, as in /77s, 
ee they are evsiform ; and if they are also sharp-pointed like 
those of most Conifers, they are acicular or acerose. A lanceo- 
Jate leaf (Fig. 153) is three or four times as long as broad; and .-».) 
