68 VARIOUS FOOD-PLANTS 
Fic. 65.—Garden Kale or Borecole (B. oleracea, var. acephala). Plant show- 
ing appearance at close of first year’s growth. x 7. (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 chlorophyll-bearing plants 
make their food are carbon dioxid (CO,.), water (HO), and 
dissolved mineral salts containing nitrogen, phosphorus, sul- 
phur, iron, potassium, ete. 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 not 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. 
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