i 4 THE BOOK OF NATURE STUDY 



life of plants is essentially like that of animals has been recognised 

 since Claude Bernard wrote his famous book, Phenomenes de 

 la vie commons aux animaux et aux ve get aux. The beech tree 

 feeds and grows, digests and breathes, as really as does the squirrel 

 on its branches. In regard to none of the main functions except 

 excretion is there any essential difference, though there are, of 

 course, great differences in detail. Many simple plants swim 

 about actively ; young shoots and roots also move ; and there 

 are many cases in which even the full-grown parts of plants 

 exhibit movement. The tendrils of the pea, the leaves of the 

 sensitive plant, the tentacles of the sundew, the stamens of the 

 rock-rose, the stigma of the musk, and many other plant structures 

 exhibit marked sensitiveness. It is instructive to take a case 

 like that of Venus's Fly-trap (Dioncza muscipula), which closes 

 its leaves on flies. There one finds not only sensitiveness, but 

 specialised sensitiveness, for the plant's tactile hairs do not respond 

 to every kind of touch ; one observes curious phenomena almost 

 like memory ; one sees rapid movement, and finds that this is 

 associated with an electrical change comparable to that observed 

 when an animal muscle contracts ; one finds a digestive ferment 

 not unlike that of the animal stomach. It is important, too, to 

 make quite clear and illustrative experiments are easy that 

 if we have in a room at night a burning candle, a growing plant, 

 and, say, a mouse, all three are using up the oxygen of the air and 

 returning to it the carbonic dioxide formed as a waste in the 

 combustion of carbon compounds. 



(V) Resemblance in Structure. The simplest plants (Pro- 

 tophyta), like the simplest animals (Protozoa), are single cells, 

 unit corpuscles of living matter (often very elaborate in their 

 own way) ; all other plants (Metaphyta) and all other animals 

 (Metazoa) are built up of numerous cells and modifications of 

 cells. In short, all living creatures have a cellular structure. 

 This general conclusion is part of the cell theory or cell doctrine 

 (1838). It may be illustrated, when a microscope is available, 

 by showing the similarity between a piece of epidermis from a 

 plant and another piece from an animal, or by comparing a 

 section of a soft stem with a section showing the supporting 

 skeletal rod (notochord) of an embryo fish. In any case, it is 



