72 THE HARMONIES OF NATURE. 



atmosphere, they are its respiratory organs, its lungs ; their 

 expansion and their number correspond with its vital activity. 

 Plants living in the shade, or restricted to a tardy growth, can 

 subsist with a few scanty leaves, but the monarchs of the woods, 

 or such plants as powerfully strive towards the sun, require a 

 vast extent of foliage to satisfy the wants of a widety-branch- 

 ing crown, or of a rapid vegetation. In a couple of months 

 the herbaceous juicy stem of the plantain shoots up as thick as 

 a man's body, to the height of fifteen or twenty feet ; but the 

 colossal leaves of the giant harmonise with this amazing rapidity 

 of growth, as they frequently attain a length of fifteen or 

 twenty feet with a breadth of two feet or more. 



As in plants of such rapid growth as the Musaceas all the efforts 

 of vegetation must necessarily tend to develope as fast as possible 

 an immense foliaceous surface, the leaves of those colossal herbs 

 are remarkably thin ; but as they are also very much exposed to 

 boisterous winds, their middle rib contains a number of ex- 

 tremely long and tough fibres, so that, although a slight breeze 

 is able to tear them into transverse shreds, by which their own 

 nutrition and their serviceableness to the plant are by no means 

 impaired, yet even a storm cannot snap them asunder ; and thus, 

 by a wonderful provision, the extreme fragility resulting from 

 an extensive growth of uncommon rapidity, is found united with 

 immense powers of resistance. 



The internal structure of the leaves is as wonderful as their 

 external variety and beauty. With the exception of such as 

 grow under water, the leaves of all the flowering or phanerogamic 

 plants are covered with a colourless cuticle consisting of cells, the 

 walls of which are flattened above and below, whilst they adhere 

 closely to each other laterally, so as to form a continuous stratum. 

 Their shape is different in almost every tribe of plants, and their 

 walls, especially on the side nearest the atmosphere, are generally 

 thickened by a waxy deposit, impermeable to fluids, the retention 

 of which within the soft tissues of the leaf is obviously the purpose 

 to be answered by the peculiar organisation of the cuticle. 



In most European plants the cuticle contains but a single 

 row of thin-sided cells, whilst in the generality of tropical 

 species there exist two, three, or even four layers of thick- 

 sided cells, which give the leaf an almost leathery consistence. 

 This difference of structure is most beautifully adapted to the 



