How the Plant Grows. 3 



per minute. Under certain conditions the upward movement of 

 water in plant stems may exceed 30 inclies per minute. 



4. How plants gather food. — Carbonic acid, which is next to 

 water in the amount utilized by plants, is taken up by them 

 through the medium of the leaves. Ten thousand volumes of air 

 contain about three volumes of carbonic acid gas; thirty- two 

 hundred cubic yards of air hold one pound of this gas. An acre 

 of growing wheat will gather during four months one ton of car- 

 bonic acid gas, or an amount equal to all the air conteins over 

 the same area of land to a height of three miles. 



In the leaves of plants, mostly on their under side, are numerous 

 minute openings leading into the interior. Air passing through 

 these carries with it carbonic acid, which is absorbed by the leaf 

 cells. The feeding roots of plants are clothed with minute haiis, 

 which take up water from the soil, together with mineral matter 

 and nitrogen compounds in solution. There are no direct open 

 ings in these root hairs, the material being taken up by difiFusion. 

 Roots are capable of dissolving and absorbing solid ingredients 

 from the soil particles with which they come in contact. Though 

 they take up some matter which is useless to the plant, roots 

 exercise a very considerable selective power in the materials 

 absorbed, and do not seem to gather plant food indiscriminately. 



5. Plant building. — Having learned what the plant lives upon 

 and how it gathers its food, let us consider how it grows. In the 

 active cells, especially those of the leaves, there is found a trans- 

 lucent, jelly-like substance called protoplasm. The life of the 

 plant may be said to exist in this protoplasm. The green coloring 

 of leaves and stems is due to a substance called chlorophyll con- 

 tained within the protoplasm. Chlorophyll is formed only in 

 sunlight. The carbonic acid gas gathered by the leaves is ab- 

 sorbed by the cells containing protoplasm charged with chloro- 

 phyll. The plant everywhere is bathed with j uices called ' ' sap, ' ' 

 a very large portion of which is water brought in by the roots. 

 Tn this sap are mineral matter and nitrogen compounds. And 

 now for the wonderful transmutation. 



The carbonic acid gas and water commingling in the cells are 

 decomposed and their atoms re -arranged and welded into a new 



