PLANTS. 65 



shapes, but each shape, no doubt, is for some defi- 

 nite purpose. A leaf may have three parts blade, 

 leafstalk, and stipules. The stipules are small leaf- 

 like appendages at the base of the leafstalk. In 

 a great many cases there are no stipules, the 

 leaf consisting of blade and petiole only. In a 

 great many more cases, the petiole and stipules are 

 both wanting, the leaf consisting of blade only. 

 The blade is the essential part of the leaf, and 

 where the leafstalk is wanting, the blade is attached 

 directly to the stem at one end, or, sometimes, 

 the stem goes right through it, either at the 

 center or at some other point. The petiole is a 

 device for carrying the leaf into free air and light, 

 so its length varies according to circumstances. 

 Some leaves turn very easily upon their petioles, 

 fluttering with the slightest breeze, and thus secure 

 every stray molecule, of passing carbonic acid gas. 



Leaf blades are either entire, or divided into 

 parts. A leaf that is smooth around its edge is 

 called a simple leaf. With some leaves, the mar- 

 gin is indented very much like the teeth of a saw. 

 Others have still deeper notches, forming what is 

 known as a lobed leaf. In another class of leaves, 

 the divisions extend clear to the midrib, forming 

 a compound leaf. 



Often a compound leaf is mistaken for several 

 simple leaves, but it can be distinguished in two 

 ways. That part which falls off in the autumn is 

 the whole leaf, and new buds for the next year's 



