filOLOGICAL PHILOSOPHY 40^ 



growth material obtained. And this food must be rendered soluble and 

 dialyzable that it may pass through membranes which surround each cell, 

 i. e. must be digested. While in the higher animal there is a place where 

 digestion and absorption occur (the digestive tract) and the digestive 

 enzymes are formed by special glands (liver, pancreas, etc.), in the plant 

 there is no such specialized tract or glands for the function of digestion 

 and absorption. There are however certain specialized tubes of cells in the 

 root, stem and leaf which taken together form "conducting paths" for the 

 water, with its dissolved salts ascending from the soil, and the sugar de- 

 scending from the leaves to root and stem, there to be stored as starch. 



From the leafy surface of humblest herb and mightiest tree, transpiration 

 takes place, or the loss of water absorbed by the roots from the soil. The 

 pressure lifting the water from the soil to the leaf may be as great in some 

 cases as that which would be exerted on the earth's surface by an atmosphere 

 six to eight times the thickness of the present one, a pressure sufficient to 

 support a column of water between two and three hundred feet high. 



Various attempts have been made to explain the rise of sap in plants but 

 as yet with no great success. The evaporation from the leaves and absorp- 

 tion of water by cells are not adequate to explain the phenomenon. (Lately 

 the cohesion of water molecules and capillarity occurring in the micro- 

 scopic stem tubes appear to offer a more reasonable explanation.) 



But can physics and chemistry explain the as yet unknown processes of 

 nervous action; the bewildering complexity of the instinct of bee or bird 

 or beast, or the yet more amazing intricacies of human thought? To an- 

 swer this question, as indeed to solve any of the problems of living matter 

 aright, it is essential that we turn to the lowest rather than to the highest 

 organism, to those which present to us in their simplest terms, all the funda- 

 mental processes of the living thing. If the extended processes or pseudo- 

 podia of an Amoeba, one of the simplest types of living things, be touched 

 with a finely drawn out thread of glass, the processes are retracted and 

 the direction of movement of the animal is altered thereby. If on the other 

 hand the Amoeba comes in contact with some object, which serves as food, 

 it reacts positively toward it, thrusting out its processes and engulfing the 

 object. Furthermore Amoeba can pursue its food, so that to the observer 

 it seems as if this tiny bit of protoplasm, so small that the largest specimens 

 appear to the naked eye as mere specks of white, were endowed with a 

 sort of primitive intelligence. 



Injurious chemicals cause Amoeba to withdraw from them. Similarly, if 

 the water on one side of the Amoeba be warmed, the animal will contract 

 on that side, and thrusting forth its pseudopodia on the other side, move 

 in the opposite direction. If a weak electric current be passed through the 

 water containing Amoeba, its behavior is similar to that under a heat stimu- 

 lus. The side toward the positive pole contracts, while from the opposite 

 side pseudopodia are extended and the animal moves toward the negative 



