WILD FLOWERS OF NEW YORK 



II 



food for the plant, gives off excess water (transpiration) and is the breathing 

 organ of the plant. To accomplish these functions the leaf is built up by 

 a complex arrangement of cells and is variously modified in different groups 

 of plants to meet the external conditions of environment and competition 

 by other plants. 



The parts of a leaf are designated as 

 blade, petiole and stipules. The leaf blade 

 (figure I A) is the broadly expanded portion, 

 although in some species the leaf blade is 

 very narrow or even threadlike. The petiole 

 (figure iB) is the stalk which supports the 

 blade, and may be lacking in some cases, when 



the leaf is said to be sessile. The stipules (figure iC) are small, leaflike 

 organs at the base of the petiole, and are best typified by the rose leaf. 

 Frequently the stipules encircle the stem at the base of the petiole and often 

 they are entirely lacking or fall away so soon after the leaves expand that 

 they are not found when the plant is in bloom. 



Terms of leaf outline: The various shapes of leaf blades may be 

 expressed by the following terms : 



Subulate; awl-shaped, withovit visible expansion of blade, and usually 

 tapering to the apex (figure 3). 



3 4 5 6 7 



Linear, or ribbon-shaped; elongated and several times longer than 

 wide (figure 4). 



