ORGANIC GROWTH. As living beings funda mentally differ from mineral bodies, so growth in plants and animals is inherently different. Even organic growth is defined as increase in volume, but this does not go far enough. Living organisms are compounds or proteids of mineral matter, forming protoplasm. and they grow by adding to the substances forming their bodies similar substances or food, which is taken within the body by interstitial deposit (intussusception), and these are digested and assimilated. This causes an increase in the volume or bulk of the body. Organic growth is fundamentally a phys ico-chemical process plus a form of constructive energy which we are unable to comprehend. In our present ignorance we invoke vital force, `growth force,' or `bathmism,' words which do not help us to understand what is behind the phenomenon of increase in volume. Besides sim ple increase in bulk, there is, as Ryder states, a process of rearrangement, further subdivision of and addition to the material basis of the organ ism. Growth, also; according' to Ryder, pro
ceeds everywhere by "adding to its substance at a rate which corresponds exactly with the rate at which the cube of the dimensions of the grow ing body is everywhere being increased. All growth is accompanied by movement, for as a cell increases in volume it becomes expanded." "Hence," says Verworn, "growth-movement§ are common to all living substance, but they take place so slowly that they can scarcely be followed with the eye." That the phenomena of growth are powerful sources of energy is exemplified by the well-known fact that trees growing out of crevices in the rock are• able by their roots to force apart huge masses of stone. See MECHANICS OF DEVELOPMENT.