ON PLANTS. 103 



causes act simultaneously on plants, they concur in pro- 

 moting the vigor of vegetation. The intensity of heat 

 tends to distend the vessels indurated by the deposition 

 of carbon, and to accelerate and give increased impetus 

 to the motion of the sap ; which, flowing profusely through 

 these firm yet still elastic vessels, produces a force of veg- 

 etation, and a magnitude of dimensions, unknown in our 

 less genial climes. 



The mountain plant, on the contrary, is peculiarly ex- 

 posed to cold ; the chilled and languid sap traverses with 

 difficulty the indurated vessels, the circulation of all the 

 juices is checked, and the vigor of vegetation propor- 

 tionally diminished. 



Caroline. And yet the flowers on mountainous plants 

 appear to me unusually large. 



Mrs. B. It is an observation which has been frequent- 

 ly made ; but I am inclined to think it is an illusion, pro- 

 duced by the comparative diminutiveness of the stem and 

 branches. 



There is a third cause of the greater hardness of plants 

 exposed to intensity of light. By assimilating a more 

 considerable quantity of carbon, the plant at the same 

 time decomposes and incorporates a greater quantity of 

 water. It is not known how this operation is performed ; 

 but the water, no longer in a liquid form, augments in- 

 stead of diminishing the solidity of the plant. 



Caroline. I should be curious to examine also, the 

 other side of the question ; that is to say, the effects of 

 a deficiency of light, such as occurs with plants cultivat- 

 ed within doors, in confined situations, in the shade of 

 forests, &-c. 



Mrs. B. In the first place, they are pale from not 

 having a sufficiency of carbon to develope their color. 

 In consequence of this deficiency of carbon, their fibres, 

 being soft and feeble, are easily stretched out, and grow 

 to a great, length ; as you may p.ossibly have seen pota- 

 toes, when sprouting in a dark cellar, shoot out weak 

 slender branches, six or eight feet in length. 



A deficiency of light diminishes the power ofevapora- 



574. How does Mrs. B. answer her objection 1 575. What fur. 

 ther is said of the smallness of mountain plants'? 576. What does Mrs. 

 B. say of the size of mountain flowers'? 577. What is a third cause 

 of the hardness of plants exposed to intensity of light'? 378. Why 

 are plants pale growing in the shade! 579. What other effect attends 

 their growing in the shade, and what is an examplel 



