PROCESS OF NUTRITION. CHAP. III. 



of succulent plants consume less than most others, 

 but they retain it also more obstinately that is, they 

 give out less carbonic acid perhaps because they 

 present fewer points of contact to the surrounding 

 air, and are furnished with fewer pores in their 

 epidermis ; hence they lose but little of their carbon, 

 even when vegetating in the open air, and can live 

 for a long time under the privation of that part of 

 their nourishment: and hence also their peculiar 

 aptitude to the different sorts of soil in which they 

 naturally grow sand, clay, or the barren rock, as 

 in the case of Sedum, Saxifrage Sempervivum. 



Plants inhabiting marshes consume less oxygene 

 than other herbaceous plants, which proceeds no 

 doubt from an institution in nature fitting them for 

 the situation in which they vegetate, and in which 

 they are deprived of the free access of oxygene, 

 owing to the vapours that surround them ; hence the 

 herbaceous plants of the mountain, where the supply 

 of oxygene is but little, are often to be found in the 

 marshes of the plain. 



The leaves of ever-greens consume also but little 

 oxygene gas, and are consequently found to thrive 

 in a barren soil, and in a rarefied atmosphere ; as in 

 the case of Pinus, Jitniperus, and Rhododendron. 



But plants which shed their leaves in the winter 

 contain in general the most oxygene, and lose, by 

 consequence, the most carbon ; and hence they are 

 not to be met with in such lofty situations as herba- 

 ceous plants. 



