CHAPTER y. 



THE SAP. 



As there is a ver^^ close similarity in the blood of all 

 animals, so does the same resemblance obtain in the 

 sap of plants. Uniformly it is limpid as water, its 

 chief constituent, and contains an acid, salts, and 

 mucilage or saccharine matter. The proportions of 

 course vaiy. 



The basis of this sap is the moisture of the soil 

 and atmosphere absorbed by the roots and other 

 organs ; and that that power of absorption is veiy 

 great has been observed in a previous chapter. 

 Neither is it an indiscriminate power : for if the 

 roots of a plant are placed in water containing two 

 or more salts in solution, they will abstract different 

 portions of those salts, and will reject some of them 

 entirely. Thus, when 100 grains of each of the 

 follomng salts were dissolved in 10,000 grains of 

 water, and plants of Polygonum persicaria, Mentha 

 jnperita, and Bidens camiah'ma were made to grow 

 in it, they took up six grains of sulphate of soda 

 (glauber salt), and ten grains of chloride of sodium 

 (common salt), but not a grain of acetate of lime. 



