75 



which is considerably denser than the surrounding 

 moisture, holding only a minute quantity of solid 

 matter in solution, we can understand that, by the 

 principle of " Endosmose," just explained, that is, 

 attraction to inwards, the moisture contained in the 

 soil enters into the most contiguous cells of the root, 

 whence it proceeds to the extremities of the plant. 

 In the leaves the fluid is exposed to the action 

 of heat, light, and air ; then chemical reaction and 

 decomposition take place under these three powerful 

 agencies, the crude fluid is converted into nutritious 

 sap, and descends by the principle of Exosmose, 

 or the flow to outwards, to the stem, depositing in 

 the various cells through which it passes the 

 different nutriments it contains, and eventually 

 discharges the useless or superfluous substances 

 through the cells of the rootlets into the soil. In 

 this way, a continual rise of crude sap and a conti- 

 nuous fall of nutritious juice occur in the system 

 of the plant, by which the necessary material for 

 the construction of its different parts is supplied. 



Some very exact and interesting experiments 

 have been made by Prince Salm Horstmar, prov- 

 ing how essential all inorganic substances are to 

 vegetable life, and how the absence of any single one 

 seriously interferes with the growth and develop- 

 ment of plants. He grew oats in a series of artificial 

 soils, each wanting one of the several inorganic sub- 

 stances which constitute the mineral food of plants ; 



