56 THE GEASSES 



and atmosphere. These elements dissolved in water begin 

 their circulation in the roots and leaves of the plant, and 

 under the influence of light, air and heat, and by the con- 

 tact with preformed protoplasm, they are gradually 

 brought over into one or the other form of this won- 

 derful substance. The instability of the juxtaposition of 

 its molecules endow it with an internal and external 

 mobility not possessed by any other body. It possesses the 

 power to arrange and re-arrange the above elements and 

 some others, when they come into contact with it, into 

 organic compounds. Protoplasm is the basis of all life upon 

 earth. 



The chlorophyll once formed, induces the respiration of 

 plants. The epidermis especially, or the leaves, which are 

 the organs of this function, possess innumerable openings, 

 stomata, through which the air passes, to be -absorbed by 

 the fluids in the tissues, and to give up to the chlorophyll 

 its carbonic acid. Now the most important chemical pro- 

 cess in the economy of the plant is effected, the carbonic 

 acid is decomposed and carbon and oxygen are mutually 

 set free. The carbon passing over into a new combination 

 with hydrogen and oxygen to form cellulose the general 

 material of vegetable fabric of cell formation. The greatest 

 part of the inhaled oxygen is returned again into the at- 

 mosphere. All the woody fibre now forming upon earth, 

 and all the coal and coal oils are derived that way. 



It is evident, that the nitrogenous and mineral constitu- 

 ents of plant food, absorbed by the roots from the soil have 

 to pass from them through the stem to the leaves. 



That some sort of circulation of fluids must take place in 

 the body of a plant, therefore, appears to be certain, but the 

 details of the process are by no means clear. There is 

 evidence to show that the ascent of fluid from the root 

 to the leaves takes place to a great extent through the 

 elongated ducts and spiral vessels that make up, together 

 with parenchymatous cellular tissue, the body of the plant, 



