2IO Elementary Biology. 



Like heat, light is a by-manifestation of kinetic energy, of 

 course connected with the general metabolism of the plant. 

 The origin and mode of development of the luminosity have 

 not as yet been satisfactorily explained. 



Electricity. The existence of electrical currents has 

 been much more carefully investigated, and numerous valu- 

 able results have been arrived at. The connection between 

 the electrical phenomena displayed and the vital processes 

 awaits, however, further elucidation. It is well known that 

 certain chemical changes are always accompanied by an 

 electrical disturbance, and probably similar chemical changes 

 in the plant metabolism give rise likewise to similar electrical 

 manifestations. The well-known carnivorous plant Dioncea 

 muscipula has been very carefully investigated, with the 

 result that a very distinct electrical current has been ob- 

 served during the folding of the leaf ; a movement which 

 takes place when the leaf is irritated by a. suitable stimulus. 

 The results of many researches on this subject may be 

 summed up in few words. During the life of a plant, 

 normal electrical currents are constantly traversing its various 

 parts, though considerable doubt prevails as to the true 

 nature of these currents, and their connection with the ex- 

 penditure of energy, which, we have seen, is so intimately 

 related with the evolution of heat and light. In addition to 

 these ordinary or normal currents, other special currents are 

 developed in parts of plants, which, like the leaves of 

 Dioncea, are capable of movement upon stimulation. In 

 these cases the electrical disturbance is undoubtedly inti- 

 mately connected with the chemical changes suddenly set 

 up in the organ by the stimulus applied. 



Among the directly visible results of the expenditure of 

 energy are, however, the very marked ones of growth and 

 movement. 



Growth. Without the expenditure of energy no growth 

 can take place, for growth is an increase in the bulk of the 

 plant, usually accompanied by a temporary or permanent 



