74 TALKS AFIELD. 



which possess leaf-green also possess the 

 power of assimilating ; that is, they can 

 make starch and similar compounds out of 

 inorganic matters, such as water and carbon 

 dioxide. Animals cannot assimilate ; they 

 eat organic products which have been pre- 

 pared by plants and digest them into other 

 organic products. Neither can all plants 

 assimilate, as we have seen in the case of 

 fungi. Plants also have a power akin to 

 digestion, for they make over the starch-like 

 materials, which are formed by assimilation, 

 into other organic compounds. This change 

 is called metastasis. The plant through its 

 roots takes in various compounds which are 

 dissolved in water. These compounds con- 

 tain carbon, hydrogen, oxygen, nitrogen, sul- 

 phur, iron, potassium, and other materials. 

 The plant takes these solutions in through 

 its roots by a modification of the phenom- 

 enon known to physicists as osmose, a sort 

 of soaking-in process. The pressure exerted 

 by the liquid as it comes into the root 

 through this osmotic action forces the "sap" 

 upwards, but the chief cause of its rise is to 

 be found in another fact: the stomata on 

 the under surface of the leaves are open if 

 the weather is clear and moist, and water is 



