CHAP, ii.] of Plants. DC Candollc. 517 



of physics and a want also of the habit of mind which this 

 imparts, and which is more important to the physiologist than a 

 knowledge merely of many facts. But this defect is still more 

 apparent in Treviranus and Meyen, whose works on physiology 

 were published soon after that of the great systematist. 



De Candolle first brings together all the facts in physiology 

 which have been discovered from the beginning, not omitting 

 the chemical researches of more modern times into the sub- 

 stance of plants, and then gives a general delineation of the 

 processes of nutrition in the plant : ' The spongioles (an unfor- 

 tunate invention of his own which has not yet disappeared from 

 French books, and plays a great part in Liebig's latest work)- 

 the spongioles of the roots, being actively contractile and aided 

 by the capillarity and hygroscopic qualities of their tissue, suck 

 in the water that surrounds them together with the saline organic 

 or gaseous substances with which it is laden. By the operation 

 of an activity which is manifested principally in the contractility 

 of the cells and perhaps also of the vessels, and is maintained 

 by the hygroscopic character and capillarity of the tissue of the 

 plant and also by the interspaces produced by exspiration of 

 the air and by other causes, the water sucked in by the roots 

 is conducted through the wood and especially in the inter- 

 cellular passages to the leaf-like parts, being attracted in a 

 vertical direction by the leaves and in a lateral direction by the 

 cellular envelope (cortical parenchyma) at every period of the 

 year, but chiefly in the spring ; a considerable part of it is 

 exhaled all day long through the stomata into the outer air in 

 the form of pure water, leaving in the organs in which the 

 evaporation takes place all the saline, and especially all the 

 mineral particles which it contained. The crude sap which 

 reaches the leaf-like parts of the plant there encounters the 

 sun-light, and by it the carbonic acid gas held in solution by 

 the sap, whether derived from the water sucked in by the roots 

 or from the atmospheric air, or being part of that which the 

 oxygen of the air produced with the surplus carbon of the plant 



