INTRODUCTION 



compound leaves, and the disposition of the leaves on the stem, and of the 

 leaflets on the petiole, are definitely related with the admission of light, 

 without which the activity of the green tissues would be much impaired, 

 if not altogether arrested. The texture of leaves is associated with the pre- 

 vention of excessive exhalation and the consequent danger from heat, and 

 among the devices adopted to shield the epidermis from the direct rays of 

 the sun, and reduce transpiration, may be mentioned the coriaceous membranes 

 with which many leaves are provided, the woolly or siliceous hair-like 

 structures which are especially prevalent on their under-surfaces, and the 

 revolute margins of many which grow in exposed situations. 



Among the contrivances adopted as a protection against animate nature 

 may be mentioned the various forms of stinging hairs, spines, and prickles to 

 be found on the leaves, petioles, stems, and branches of various plants. In 

 the struggle for existence, and in the face of the incessant depredations of 

 animal visitors, these modifications of plant structures have undoubtedly 

 been the salvation of the race. In the case of the lower forms of animal 

 life, more especially as regards the insect world, the signs of warfare are 

 many and numerous, whole colonies of trees and shrubs sometimes being 

 denuded of foliage by insect larvae, and volumes have been devoted to the 

 description of the various galls which owe their origin to insect agency. 

 Many of these attack the leaves, and attention is drawn to a few in the 

 descriptive pages. The foliage also is especially susceptible to fungoid diseases, 

 and an interesting study may be made of these at all seasons of the year. 

 The life-history of many is at present but imperfectly known, and a wide 

 field of research here lies open to the earnest worker. 



AUTUMNAL BEAUTY OF HEDGEROW, WOOD, 



AND GARDEN 



Before leaving this part of our subject we will for a moment direct 



attention to the autumnal beauty of our hedges, woods, and gardens. Few 



dwellers in the country can have failed to notice the infinite variety of 



colour which attaches to the dying foliage, and even those in towns must 



xiv 



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