Mben tbe lIUlooDs are %caUQVcc\i 73 



seeds being perfected, the work of the j^lant for the 

 year is accomplished, and the root-mouths are less 

 active. The capillary vessels and the leaf-cells no 

 longer force sap through the plant. Unfed by sap, 

 too much clogged to feed from the air, the leaf fades. 

 At the axils of the leaves the buds for next spring 

 are formed, and thus by surfeit and by pressure the 

 old leaf is severed from the parent stem. This is 

 rendered more easy by a peculiar construction of the 

 cells at the foot of the leaf-stem. 



Properly to perform their offices, leaves need 

 abundant light and air. If they grow under water 

 or in dense hedges, where tlie supply of air and sun- 

 shine is limited, new plans must be laid for securing 

 what is indispensable. We find that leaves growing 

 in such situations are ver}^ finely divided, even when 

 in other conditions the plants bear leaves but little 

 divided. Where great economy is demanded, at 

 once the plant forms deeply-divided leaves which 

 shall act as a seine to intercept as much as possible 

 of the light, air, and moisture demanded for convert- 

 ing crude sap to plant-food. Tlie additional surface 

 secured by these repeated divisions makes up for the 

 harder circumstances of their lives. 



Organs so valuable as leaves must be protected. 

 Leaves are sometimes defended l)y sharp prickles, as 

 in the cactus, thistle, holly ; l^y rough coats, as the 



