Leaves of 



Young 



Plants. 



Other 

 Characters 

 of Leaves. 



Such aerial stems are usually surrounded by brighter light 

 than are the creeping stems and their leaves are exposed not 

 only to overhead light, but also to considerable lateral 

 illumination, so that in their case the partial shading of the 

 lower leaves by the upper ones is not so important, the loss of 

 overhead light being compensated by the addition of lateral 

 light. Moreover as in such stems plenty of room is available 

 to enable the leaves to develop at different levels it is not so 

 necessary that the leaves arising at any one level should fit 

 together closely and accurately, for the light which passes 

 through the interstices of the upper leaf-layers may be received 

 and utilised by the lower leaves and is not therefore lost to 

 the plant. Hence in these shoots leaves of such size and shapa 

 as are necessary to form a close-fitting, more or less flat, 

 mosaic are not required. 



Although hete^ophylly is one of the expedients resorted to 

 by plants in order to have as large a leaf surface as possible 

 exposed to the light, it is by no means the only one, and in other 

 plants the same end may be attained in a variety of ways. 



25. The leaves of seedlings and 



young plants usually differ considerably from those of mature 

 plants. Fig. 5, Plate XII, shows a seedling of Oroxylum 

 indicum and indicates the difference which may exist between 

 the first leaves and those subsequently developed, for the 

 leaves there shown bear not the least resemblance to the 

 enormous bi- and tri-pinnate leaves of the mature tree. 

 The leaves of young pfants of Quercus semecarpifolia have 

 spines and are toothed, while on old trees they are usually 

 entire, and in Gardenia turgida the leaves of young plants 

 are quite unlike those of older plants. In species of Phcenix 

 the leaves of young plants are usually entire while those 

 of mature plants are pinnate. Similarly the leaves on coppice 

 shoots often differ considerably in size and shape from 

 those on uninjured plants. On coppice shoots of Pyrus 

 Pashia the leaves are often lobed or cleft, whereas they are 

 normally crenate. This point is one of practical importance 

 for Foresters, who, unless they are able to recognise their 

 trees and shrubs at different stages of their life-history, can 

 know very little about the reproduction of their forests. 



26. Leaves may be glossy or 



shining, like those of Cocculus laurifolius, or dull and not 

 shining like those of Euonymus Hamiltonianus and in this, 

 as in other respects, the upper and lower surface of the leaf- 

 blade may differ considerably. As regards colour, mature 



