416 



RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. 



themselves, that is to say, more or less horizontally, and increase in length in 

 this direction until their leaves project outside the shadow of the topmost leafy 

 branches, so that they may be able there to catch the sunlight. All this is 

 observed not only in maples, which have been selected as examples, but in all 

 richly -leaved trees and shrubs; the topmost branches are directed vertically 

 upwards, the next lower rise obliquely, those still lower extend horizontally, 

 and the lowest of all frequently even incline earthwards. The twigs of the 



older, lower branches 

 which have grown 

 out beyond the 

 shaded area often 

 again try to rise, 

 and assume a direc- 

 tion which is almost 

 similar to that of 

 the highest branches 

 at the summit. Such 

 branches and twigs 

 then display a cur- 

 vature which is like 

 a Roman f\J lying 

 sideways. Oaks and 

 horse-chestnut trees 

 furnish striking 

 examples of this. 

 The phenomenon is 

 shown still better 

 in firs (see fig. 105), 

 in which the twigs 

 springing from the 

 lowest branches fre- 

 quently rise almost 

 vertically. This last circumstance is also of interest in so far as it indicates 

 that it is not only the weight of the leaves which brings about the altered 

 direction of the branching, but that it depends also on other conditions, to be 

 discussed later on. 



In the terminal twigs of the lowest branches, which are again turned upwards, 

 the same distribution and direction of the leaf-blades as are displayed by the 

 erect twigs of the summit will naturally be resumed; but it is not so in the case 

 of those twigs which retain a horizontal direction, or whose summits are even 

 inclined towards the ground. Suppose that the maple-twig, which is illustrated 

 here, has not grown from a central bud of the summit, and does not rise vertically 

 upwards, but that it has been developed from an older, lower branch, and is extended 



Fig. 106.— Erect leafy Twig of the Norway Maple (Acer platanoides) 



