ILLINOIS NATURAL HISTORY SURVEY MANUAL 1 
which has many forms but in the majority of cases is broad, 
thin and flat, so as to provide a large surface for absorption of 
the light that is needed in manufacturing plant food, and for 
water loss by evaporation. The petiole, if it is present, is the 
stalk by which the blade is attached to the stem. The base of 
the blade is its usual place of attachment to the petiole, but the 
attachment may be to the under surface as in the garden nas- 
turtium, in which case the leaf is said to be peltate. Stipules 
Fig. 2.— LEAF MARGINS AND VENATION. a.—Pinnately veined, 
lobed leaf of oak. b.—Palmately veined, toothed leaf of nettle. 
c.—Netted-veined, doubly toothed leaf of elm. d.—Parallel-veined, 
entire leaf of false Solomon’s seal. 
are the outgrowths, frequently leaflike, from either side of the 
petiole base. 
Leaves may be modified into forms not easily recognized, 
as, for example, the spines of cactus and the scales of the onion 
bulb. Quite commonly they retain a familiar shape but are 
incomplete by absence of stipules, petiole or both. On many 
kinds of leaves no stipules develop, from others they drop when 
the leaf is young, and on the complete leaf they persist, of 
course, through maturity. The fine scars on the stem at the 
bases of the petioles, left as the stipules drop off, are called 
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