2 BOTANY 



all assimilate food substances from without, which undergo profound 

 chemical changes before they are incorporated with the substance of 

 the organism, which by virtue of this food-assimilation grows ; they 

 respire, i.e. develop energy by the decomposition of complex sub- 

 stances through oxidation, or occasionally otherwise ; finally, they 

 always show some form of reproduction by which new individuals 

 are formed. 



Thus a flowering plant absorbs through its roots water and various 

 dissolved mineral constituents, and through the stomata, small open- 

 ings in the epidermis of the leaves, takes in carbon-dioxide from the 

 atmosphere. By virtue of energy derived from sunlight, the green 

 cells of the leaves are able to decompose water and carbon-dioxide, 

 from which they manufacture the elementary organic compounds 

 which are needed to build up the tissues. Oxidation of the tissues, 

 resulting in the evolution of heat and giving off of water, accom- 

 panies all the vital activities. This respiration is not as active in 

 green plants as it is in animals, but is otherwise much the same. 



For a long time sometimes many centuries the assimilation of 

 food exceeds the loss through respiration and otherwise, and the 

 plant increases in bulk. Finally the growth declines and the plant 

 dies. During its active growth provision is made for continuing the 

 species, either by the separation of buds from the parent plant, or by 

 the formation of seeds. 



While movement in the higher plants is seldom conspicuous, a 

 study of the behavior of the plant will show that movement of 

 various parts is often easily demonstrable. 



Protoplasm. In living tissues there is invariably present a pecul- 

 iar substance, protoplasm, with which all vital functions are asso- 

 ciated, and which has, therefore, very aptly been termed the physical 

 basis of life. 



Every living organism is a factory in which there is a never-ceasing 

 'production of substances which help to build up the body. This is 

 accompanied by the formation of waste-products, which may, how- 

 ever, serve as food for other organisms. 



Sources of Energy. In order that these vital processes may be 

 maintained, a supply of energy is necessary, and this is furnished 

 either by the decomposition of organic food, or, in the case of green 

 plants, directly by the sun's rays. So far as we certainly know, only 

 such organisms as possess the peculiar green pigment, chlorophyll, 

 or leaf -green, or its physiological equivalent bacterio-purpurin, have 

 the power to assimilate the carbon-dioxide of the atmosphere, which 

 is the ultimate source of all the carbon in the cells of plants and ani- 

 mals. The green cells absorb the light-rays whose energy is employed 

 in the decomposition of CO 2 and water, and the manufacture of the 

 primary organic carbon compounds, of which starch and sugar are 



