96 



HUTCHINSON'S POPULAR BOTANY 



Photo by-] 



FIG. 130. ROUND-LEAVED SUNDEW (Drosera rotundifolia). 



IE. Step. 



A larger species than the last, growing in similar situations and with the same habits. Reduced about one-third. 

 N. EUROPE, W. ASIA, N. AMERICA. 



the plants which exist upon the earth. Submerged plants, having no 

 direct contact with the atmosphere, derive their carbon from the carbon 

 dioxide -dissolved in the water in which they live. 



Carbonic acid is a gas consisting of two elements, oxygen and carbon, 

 combined in the proportion of two atoms of oxygen to one of carbon (C0 2 ) ; 

 and as the former is another of our plant elements, it is evident that carbon 

 is not the only nutrient substance taken up by the leaves. Yet by no means 

 all the oxygen required by the plant enters in through these organs. A 

 large proportion is obtained from the water absorbed by the root-hairs, 

 which, indeed, are the organs employed in conveying most of the food 

 substances to the plant ; and this taking in of inorganic nutrient matter by 

 the root-hairs is known as absorption. 



Then there is hydrogen. Oxygen combines with hydrogen in a certain 

 proportion (H 2 0) to form water ; so that when the roots are drinking up 

 water from the ground they are taking in two of the most essential elements 

 of the plant. It is probable, however, that a good deal of the hydrogen 

 supplied to the plant enters it in combination with nitrogen (another of the 

 essential elements of all plants) in fact, as ammonia (NH 3 ), that pungent 

 gas which gives strength to hartshorn and smelling-salts, and which is 

 dissolved in the water absorbed from the soil. 



