Vegetal Evolution. 149 



the scale for either animal or vegetal life, viz., the 

 composition of the organism's external membrane. 

 If this envelope be albumen — a flexible substance — 

 the protoplasm manifests motion externally through 

 pseudopodial projections ; hence the organism appears 

 as an animal. If the membrane be cellulose — a firm, 

 tenacious substance — external motions are impracti- 

 cable, internal motions alone supervene, and the 

 organism develops as a plant. A more important 

 magnetic distinction, however, is noticed anon. 



(9) Functions of Plants. — The chief functions per- 

 formed by all plants are nutrition and reproduction. 

 The organs of nutrition are the roots, stem, and 

 leaves ; while the organs of reproduction are the 

 flowers, or their equivalent inflorescences. In the 

 lowest plants none of these organs are adequately 

 represented, yet all absorb nourishment and repro- 

 duce. 



(a) Nutrition. — Nearly all flowering plants have 

 the usual organs of nutrition, but infinite differences 

 pervade their forms. The root absorbs liquid food 

 containing nitrogen, phosphorus, sulphur, potassium, 

 iron, etc. These elements, either pure or combined, 

 it first extracts from the soil, then absorbs, and finally 

 flushes through its whole organism ; the ducts being 

 the cells, the cell-walls, and the vessels. The root, 

 like the rest of the plant, is composed of cells, but 

 the nourishment is imbibed by the root-hairs, which 

 are merely prolongations of those cells which form 

 the epidermis of the root-fibres. The stem and 



