Page:Life Movements in Plants.djvu/173

Rh 8ays, " In the phenomenon of metabolism, two processes must be distinguished, the building up of a complex system or substance of high potential energy, ' anabolism,' and the breaking down of such a system ' catabolism,' giving off energy in other forms. The tendency of much recent work, however, is to throw doubt on the universality of this opposition of anabolism and catabolism as explana- tory of physiological activity in general."

The results obtained with the response of plants to stimu- lus may perhaps throw some light on the obscurities that surround the subject. They show that the two pro- cesses may be present simultaneously, and thai the ' down ' change induced by stimulus may, in certain instances, be more than compensated by the ' up ' change. I shall, for convenience, designate the physico-chemical modification, as- sociated with the excitatory negative mechanical and elec- trical response of plants, as the " D " change ; this is attend- ed by run down of energy. The positive mechanical and electrical response must therefore connote opposite physico- chemical change, with increase of potential energy. This I shall designate as the " A " change, which by increasing the latent energy, enhances the functional activity of the tissue. That stimulus may give rise simultaneously to both A., and D, effects, finds strong support in the dual reactions ex- hibited in plant-response. Under indirect stimulus, the two responses are seen separately, the more intense negative following the feeble positive. When by the reduction of the intervening distance, stimulus is made direct, the result- ant response, as previously stated, is negative ; and this is due not to the total absence of the positive but to its being masked by the predominant negative. Let us next