HOW PLANTS GROW 



the air. Some oxygen gas is, however, being continuously absorbed by 

 all green plants and is necessaiy for their growth. 



The mineral substances, such as phosphates, potash, and lime, which 

 are needed by the plants, are taken from the soil thru the roots. 



Plant building. — The carbon dioxid, the water, and the nitrates and 

 other mineral compounds are carried in the sap currents to the living, 

 green-colored protoplasm of the leaf cells. Here these relatively 

 simple compounds are built into the much more complex plant sub- 



FiG. 3. — Plant Cells, Magnified 350 Times 



A, Cell wall; b, nucleus, or life center of cell; c, strands of protoplasm; d, 

 spaces filled with cell sap; e, chlorophyll bodies. (After Strassburger. ) 



Fig. 4. — Section op Leaf, Magnified 400 Times 



A, stoma, or openings on under side of leaf thru which air enters; b, chloro- 

 phyll bodies in leaf cells; d, lower epidermal cells of leaf; e, upper epidermal 

 cells of leaf. (After Strassburger.) 



stances. In some mysterious manner chlorophyll, the green coloring 

 matter of the leaves, breaks down carbon dioxid and water under the 

 influence of light, and rearranges the carbon, hydrogen, and some of 

 the oxygen into relatively simple plant compounds. The rest of the 

 oxygen is given back to the air as free oxygen gas. It is not definitely 

 known whether the first product so formed is starch, sugar, or some 

 simpler compound. From the compounds first made the plant then 

 builds more complex substances, some of which contain mineral matter 

 obtained from the soil. Both sugar and starch contain much energy, 



