PLANTS 



The continued existence of such life as is familiar to us 

 depends upon the acquirement of external energy. At the sur- 

 face of the earth the most available source of energy is the sun's 

 rays. Acting through the chlorophyl, — the green coloring mat- 

 ter of plants, — this energy of the sun breaks up the inorganic 

 components of earth, air and water into their separate elements 

 and then recombines them into the potential or stored-up energy 

 of foodstuffs. Plants expend this energy largely in reproduction, 

 — in the development of spores and seeds. Animals, on the 

 other hand, make use of this energy stored up by the plants, 

 expending it in free movements as well as in reproducing their 

 kind. In the lowest divisions of each kingdom, however, — ^the 

 .thallophytes of the plants and the protozoons of the animals, — ■ 

 still occur individuals, such, for example, as the protozoon, 

 Euglena, which combine both methods of energy getting. 



The food of plants consists principally of inorganic salts and 

 carbon dioxid in solution in water; this is absorbed by the 

 protoplasm of the plant. In the case of the unicellular plant, 

 the whole plant body surrounds the food and absorbs it, while 

 among higher plants the roots and rootlets are differentiated to 

 perform that function. In higher plants the taking up of excess 

 liquid, or the contraction of the intaking cells, forces this food 

 solution up through tubes which are arranged in bundles (vas- 

 cular bundles). Under the influence of the sunlight the carbon 

 dioxid is broken up into the gases carbon and oxygen ; the former 

 after being combined with the inorganic substances is transferred 

 to the growing parts of the plant through other tubes in the 

 vascular bundles, while the oxygen is thrown off. Parasitic 

 plants, such as the fungi and bacteria, are exceptional in that 



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