48 



PLANT STUDIES 



small jjlaiits growing in exiiosed situations, as bare rocks 

 anil sandy ground. The cluster of leaves, flat upon tlie 

 ground, or nearly so. and more or less overlajiping, is very 

 effectively arranged for resisting intense light or drought 

 or cold (se(^ Figs. ] I. 1'?. 4S). 



oS. Protective positions. — In other cases, a ])osition is 

 assumed liy the lea.ves wlni^h directs their flat 

 surfaces so that tliey are not exposed to the 

 most intense rays of light. The so-called " com- 



Fk;. -Jl. A leaf of a sensitive plant in two conditions. In the figure to the left the 

 leaf is fully espandetl, with its four main divisions and numerous leaflets well 

 spread. In the figure to the right is shown the same leaf after it has hecn 

 "shocked" hy a sudden touch, or by sudden heat, or in some other way. The 

 leaflets have been thrown together forward and upward ; the four main divisions 

 have been moved together ; and the main leaf-stalk has been directed sharply 

 downward. The whole change has very much reduced the surface of exposure. — 

 After DucHARTr.E. 



pass plants," already mentioned, are illustrations of this, 

 the leaves standing edgewise and receiving on their surface 

 the less intense rays of light (see Figs. 5, 170). In the 

 dry regions of Australia the leaves on many of the forest 

 ti'ccs and shruljs havc^ this characteristic edgewise position, 

 known as ihe jirofile position:, giving to the foliage a very 

 curiotis a.jipcarance. 



Some leaves have; the jiower of shifting their ])osition 

 aecording to their needs, directing their flat surfaces to- 

 ward the light, or more or less inclining them, according 



