68 



VARIOUS FOOD-PLANTS 



•Fig. 65. — Garden Kale or Borecole {B. oleracea, var. uccphala). Plant show- 

 ing appearance at close of first year's growth, x ^. (Vilmorin.) 



of showing two colors — green when the light shines through 

 it, and red when the surface is strongly illuminated. 



The raw materials out of which chlorophjdl-bearing plants 

 make their food are carbon dioxid (CO.j), water (H2O), and 

 dissolved mineral salts containing nitrogen, phosphorus, sul- 

 phur, iron, potassium, etc. The carbon dioxid, known as 

 carbonic acid when dissolved in water, is a gas which forms 

 about one twenty-five-hundredth of the atmosphere, and 

 a somewhat larger proportion of all the natural waters of 

 the earth. It is being breathed out continually by plants 

 and animals, and so would increase enormously in amount 

 were it hot absorbed by the green parts of plants. Five per 

 cent of the gas mixed with air acts like a poison when breathed 

 in by animals, but even larger amounts are quite harmless 

 to plants. 



