INTRODUCTION. 



soon, however, as it reaches a moist situation, it sends down its 

 roots into the soil, and unfolds to the atmosphere its leaves, 

 which, from a dingy brown, speedily change to the bright green 

 of active vegetation. The Rose of Jericho is the subject of 

 similar transformations; and the common Mosses exhibit the 

 same in a less degree. 



These conditions are not the only ones admitting of great 

 variation, and yet most important to the active operations of the 

 vegetable structure. Light is as important as warmth and 

 moisture to the processes of the economy; and yet we find plants 

 adapted to thrive under the almost total deprivation of it. Sea- 

 weeds possessing a bright green colour have been drawn up from 

 the depth of more than 100 fathoms, to which the sun's rays do 

 not penetrate in any appreciable proportion. Many of the 

 Mushroom tribe have been found growing in caverns and mines, 

 to which no rays from the sun, either direct or reflected, would 

 seem to have access ; and even more perfect plants have been 

 observed to vegetate, and to acquire a green colour (which is in 

 general only produced under the influence of strong light), in 

 such situations. On the other hand, we find some plants adapted 

 only to exist, where they can be daily invigorated by the powerful 

 rays of a tropical sun, with the complete daily change which 

 results from their total absence, during a large part of the twenty- 

 four hours; whilst there are others whose energies, after re- 

 maining dormant during the tedious winter of the arctic regions, 

 are aroused into a brief activity by the return of the luminary on 

 whose cheering influence they depend, and whose rays are not 

 withdrawn from them for weeks or even months together. 

 Neither of these tribes could flourish, if transferred to the cir- 

 cumstances of the other; and, opposite as these circumstances 

 are, we observe that the Creator has adapted living beings to 

 inhabit each, with equal suitableness. 



This adaptation of each species to particular circumstances, is 

 often seen in an interesting manner on a small scale, on the ex- 



