136 OUTLINES OF PLANT LIFE. 



Plant foods, like animal foods, belong mainly to three groups, carbo- 

 hydrates, fats, and proteids. Examples of the first are the sugars, of 

 which grape sugar, fruit sugar, and cane sugar are the commonest ; 

 starch, which can be broken up into grape sugar ; and cellulose, the 

 material of cell-walls. Examples of the fats are olive oil, palm oil, cot- 

 ton oil, etc. Proteids are generally recognizable by their property of 

 coagulating upon application of heat, acids, etc. Examples are the 

 albumen of "white of egg," the fibrin of blood, casein of milk, etc. 

 Examples from plants are abundant, but less generally known. Proteids 

 always, and either carbohydrates or fats, or both, must be available in 

 order that a plant may be properly nourished. 



Green plants obtain their food chiefly by manufacturing it 

 out of simple materials taken into the plant body from the 

 soil and air. They are the only living things, so far as 

 known, which have the power of building up foods out of 

 such simple materials as carbonic acid gas and water. They 

 are, therefore, the ultimate source of the food supply of the 

 world. 



C. Nutrition of colorless plants. 



180. Colorless plants. — By this really inaccurate phrase 

 are meant plants which do not possess chlorophyll, though 

 some of them are highly colored by other pigments. 



The colorless plants among the thallophytes constitute two 

 large groups, known as bacteria and fungi. Among the seed 

 plants, also, are found some de-void of chlorophyll. 



Many plants possessing chlorophyll show to the eye other 

 tints than green, when other pigments are present in such 

 quantity as to mask the green. This is notably the case with 

 the so-called "foliage plants," in which reds, yellows, 

 purples, and browns are common.' (See also T^ 9, 33, 38.) 



Colorless plants necessarily live either upon the material 

 once produced by a living being, oftentimes upon its dead 

 and decomposing body, or in company with living organisms. 

 Those which live upon dead bodies, whether these have lost 



