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394 development of new forms, but also in physiological differentiation, that is, in the development of specialised mechanisms for the performance of the various vital functions. There still exists a long prevalent idea that physiological mechanisms of animals and plants are fundamentally different. The evidence afforded by results of experimental investigations show that this idea is unfounded.

The most important characteristics of certain animal tissues are (1) contractility on account of which rapid movement is produced by muscular organ; (2) conductivity or power of transmitting excitation to a distance and (3) rhythmicity or so called spontaneous movements.

Muscular organ in plants.—The functional similarity between the two contractile organs, pulvinus and muscle, is not confined to the manifestation of outward movement, but can be traced to the ultimate protoplasmic mechanism. There are three types of contractile organs distinguished by their rapidity of reaction. The wing-muscle of a bird of prey like the falcon is very active; that of the goose is less active, while the muscle of the domestic fowl is almost inactive, its power of flight having been practically lost. The activity of animal muscle is found to be dependent on the presence and relative distribution of an active substance.

In the leaves of plants there are similarly three types of motor organ—active, semi-active and inactive. The first is exemplified by Mimosa pudica, the second by Neptunia oleracea; and the third by the pulvinus of Phaseolus in which the movement is very feeble and extremely sluggish. By means of selective staining I succeeded in producing a sharp differentiation of the