with Geographic Botany. — Light. 471 



the tree? shed their leaves, leaving no tender organs exposed^ 

 vitahty is well shut up and preserved in the solid parts, and 

 the perennial plants leave their roots buried within the slow 

 conducting materials of the earth. 



Light is not so essential to colours but that they are some- 

 times produced without it, and all which in botanical accep- 

 tation are received as such, are known to be developed with- 

 out its influence ; green, which is not regarded botanically as 

 a colour, is the most rarely formed under such circumstances ; 

 but instances are to be met with, and I shall cite the rich 

 green of the seeds imbedded in the pulp of the fruit of the 

 Jacquinia aurantiaca. Many sea-weeds, growing at depths 

 accessible only to very subdued light, are supplied with much 

 richness of colour, good pinks and greens being the most 

 common. Plants will sometimes grow where they are not in 

 the least degree exposed to light, and even in such cases they 

 will form a small portion of chromule ; their general appear- 

 ance is here so changed and distorted that they are not easily 

 recognized, the organs being irregularly developed, and losing 

 their customary shape and outline. In a natural state the 

 simpler organized plants are more usually found in situations 

 feebly admitting light, as mosses, lichens, and the Algce gloio- 

 cladece. 



The good effects of light on the vegetable kingdom are dis- 

 played in a variety of ways connected with its growth ; it in- 

 creases the stature and development of forest-trees, causing 

 them to spread more, giving a greater solidity to their struc- 

 ture, and strength and durability to their woods. In those 

 countries where the brilliancy of the light is not obstructed 

 by atmospheric causes, the flowers excel in the lustre of their 

 colours, and vegetation partakes strongly of fragrance: Lower 

 Cahfornia, though destitute of trees and almost of shrubs, has 

 a variety of plants of the most lively colours, and both the 

 flowers and foliage generally abound in aromatic properties. 

 The absence here of the larger vegetation admits freely the 

 sun^s rays ; the dew-point of the atmosphere is greatly below 

 the temperature, there being but little suspended moisture, 

 the skies cloudless, and the soil too arid to admit of much 

 evaporation. The vegetation, though consisting entirely of 

 lowly plants, is exceedingly interesting from the engaging 

 colours, peculiar structure of many of the flowers, and the in- 

 dividuality of the flora generally. 



In one state of vegetation alone is light prejudicial ; during 

 germination carbonic acid is given off by the seed and oxygen 

 absorbed : this is a state of things favoured by darkness, the 

 reverse occurring in growing plants when exposed to the 



