CONDITIONS FOR THE GROWTH OF PLANTS. 23 



be very great. A certain amount of oxygen, how- 

 ever, must be present in the air, to permit the 

 continued growth of the plant ; for most plants will 

 not grow in an atmosphere of pure carbonic acid gas. 



The hydrogen needed for the plant's growth is 

 derived from the decomposition of the water asso- 

 ciated with the carbonic acid; the result is that 

 the plant retains the carbon and the hydrogen, and 

 throws out the oxygen into the atmosphere. 



3. Mineral matters taken from the soil. 



The tissues of the plant contain various kinds 

 of mineral substances which are taken directly 

 from the soil. For the proper growth of the 

 plant, the soil must contain these particular min- 

 eral substances in the condition or state in which 

 they can be readily taken up or assimilated by the 

 plant. 



The above conditions viz., the germ, the cradle, 

 the sun's light and heat, and some form of solid 

 and liquid food are not of equal importance to 

 the growth of the plant. 



The presence of the germ or seed is, of course, 

 of the greatest importance, since without it no 

 plant can grow. 



The sunshine and the heat may, perhaps, be 

 considered as next in importance to the growth 



