Minnesota Plant Life. 491 



cores in which they are deposited as starch or as oils. Proteid 

 substances, originating also in the foliage of the green plant, 

 may be carried away in the form of peptones to growing tracts, 

 or to storage organs, where they may take the shape of little 

 granules, known as farina grains or aleurone grains. Storage 

 layers commonly occur along the conduction-paths, while spe- 

 cial storage organs are produced in a variety of plants. Of 

 such storage organs an ordinary potato, onion, beet or carrot 

 may serve as familiar examples. 



Ultimate disposal of the food. The materials taken into the 

 body of the plant and subjected to the elaborative processes 

 initiated by the living substances must be either retained as 

 part of the body or excreted. The high manifestation of energy 

 that characterizes the animal is by no means so characteristic 

 of the plant. In other words, constructive processes prepon- 

 derate in the plant-\vorld and a greater proportion of material 

 received as food remains in the body of the plant than in the 

 body of the animal. Excrements are, therefore, not so abun- 

 dant among plants as among animals. Indeed the principal 

 plant excreta are gaseous. From the leaves are given off 

 oxygen, a waste-product of starch-making, and water vapor. 

 Water in the fluid state is also rejected by many plants. Car- 

 bonic-acid gas, a waste-product of respiration, is excreted from 

 the surface of the plant, both in the area of the shoot and of 

 the root. Solid excreta, however, are not formed by plants. 



When retained in the body of the plant, food materials may 

 assume a great variety of forms. A certain portion is utilized 

 in the production of new living substance, but by far the greater 

 .amount is stored as cellulose, bark-substance, wood-substance, 

 gelatine, crystals, organic acids, coloring material, tannin, alka- 

 loids, glucosides, oils, fats, resins, gums, reserve-food and cell 

 sap. Many thousands of plant products are known, so marvel- 

 ous is the chemical activity of the living substance. 



Growth. The term growth is rather an ambiguous one, since 

 it is applied in several different ways. It should at least ex- 

 clude nutrition, and should generally indicate increase in size. 

 Sometimes, however, there may be an increase in mass without 

 a visible increase in size, and it seems difficult in such an in- 

 stance not to apply the term growth to the process of enlarge- 



