of tubes. This conclusion, however, disregards many well-known adverse facts. Thus it is possible to secure the conduction of an impulse through a section of stem, one or even two centimeters in length, which has been killed by a steam jacket and allowed to desiccate. Then again, when excised stems have been placed in connection with the most powerful force pumps, or the action of the strongest osmotic solutions, and artificial disturbances set up, no reactions were induced in the pinnules, although great hydrostatic movements must have been initiated. The above mentioned hypothesis must be declared 'not proven,' although it is a puzzling matter to attempt any suggestion of a method by which transmission could be accomplished through 2 cm. of dead tissues, and a meter of living tissue.
Fig. 5. Fibrillar Structures in Cells of Plerome of Root of Onion supposed by Nemec to transmit Impulses.
Nemec finds a somewhat regular coincidence of fibrillar structures in the apical portions of roots, with the pathway which impulses should travel in passing from the perceptive region to the motor zones. The occurrence of these structures has been well known for some time, and the theory of their function as special transmitting organs has something in its favor, especially as these fibrillae have continuous intercellular communications. No facts are at hand to suggest the presence of these fibrillar organs in other members of the body.
The decentralized organization of the plant, the intimate and delicate morphogenic and physiologic correlations existing among all its members and its reflective system of irritability, make unnecessary, and preclude, the differentiation of transmitting tracts, except in certain narrowly specialized organs adapted to other than their typical vegetative purposes. The most recent hypothesis as to the geotropic action of the
Fig. 6. Statolithic Action of Cells of Stelar Sheath containing Starch, by the Aid of which Equilibrium is supposed to be maintained.
plant is in accordance with these ideas. By this theory the maintenance of equilibrium is made possible by the appreciation of gravity as the result of the position of granules in sheath cells in every part of the body, these cells acting as statoliths and sending impulses to the motor zones of the organs in which they are found.