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 ot 

 the Hght 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 ot the 

 petiole base. 



Leaves may be modified into forms not easily recognized, 

 as, for example, the spines of cactus and the scales ot 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, ot 

 course, through maturity. The fine scars on the stem at the 

 bases of the petioles, left as the stipules drop off, are called 



