: 
4 
4 
4 
: 
4 
3 
THE LEAF Zio 
spongy-parenchyma and border parenchyma regions, and stomata are 
only found in the lower epidermis. 
The Petio.e is the leaf stalk which supports the lamina in a 
position where it will receive the most light for photosynthesis. 
The Sriputes are leaf-like appendages appearing at. the base 
of the petiole. 
The leaf of the Slippery Elm (Ulmus fulva) affords a good 
example of a Complete Leaf (see Fig. 150). 
7 
oY es 
& 
9 sew $02 
Ww wi. 
5 @ 
rg 0 
oO 6 @ ; (Kirt > 
: WALI ZA 
% 8 \\\SR8 xo 
o : oe f 86 2 =s 
Fic. 152.—Camera-lucida drawing of a tangential section of a leaf (section 
parallel to leaf surface) showing /f, intercellular-air-spaces between the palisade par- 
enchyma cells (e); g, border parenchyma; h, tracheal elements of a vein. (Stevens.) 
Sometimes the lamina or blade is attached directly to the 
stem by its base and the leaf is then said to be sessile. If the 
petiole is present, the leaf is petzolate. 
When leaf stipules are absent, the leaf is said to be exstipulate; 
when present, stzpulate. 
The petiole is seldom cylindrical in form, but usually chan- 
nelled on the upper side, flattened, or compressed. The stipules 
are always in pairs and closely resemble the leaf in structure. 
Lear Functions.—The most essential function of green plants 
is the conversion of inorganic into organic matter; this takes 
place ordinarily in the green parts, containing chlorophyll, and 
in these when exposed to sunlight. Foliage is an adaptation 
for increasing the extent of green surface. 
