GENERAL VIEW 401 



certain cases, although when the freezing of water produces frost-cracks, 

 the liberation of energy is excessive and beyond the plant's power of 

 control. According to the conditions and to the point of view energy 

 produced by the precipitation of a solid or by crystallization may be 

 regarded as a manifestation of volume energy, of chemical energy, or of 

 surface-tension energy 1 . 



Work is done during all movements in overcoming the resistance 

 of surrounding media and in displacing internal parts. In the latter case 

 the work done may be stored up in the form of potential energy capable 

 of sudden liberation, as in the tissue-tensions, in the pulvinus of Mimosa, 

 the leaf of Dionaea, and various suddenly-dehiscing fruits. The upright 

 growth of a shoot involves the storage of a certain amount of potential 

 energy, which is manifested as kinetic energy when the trunk is sawn 

 through, and is transformed mainly into heat when the trunk falls upon hard 

 ground. The total amount of energy involved here is, however, trifling as 

 compared with that represented by the raising of water during transpira- 

 tion, and by the kinetic resistance which the ascending stream has to 

 overcome. 



The law of the conservation of energy and of mass holds good during 

 all the transformations of energy in the plant. The energy stored up 

 during life is ultimately set free on death either by decomposition, com- 

 bustion, or by being drawn into the metabolism of some other organisms. 

 There is no reason for assuming the existence of any special form of vital 

 energy, since the same form of energy may produce the most varied results 

 according to the mechanism on which it acts. The capacity of the organism 

 for continued and automatically regulated growth and the hereditary 

 tendencies of the germ -cells enable the offspring to employ the energy and 

 food-materials in the same manner as the ancestors. Hence the species 

 may remain unaltered although the descendants may contain not a single 

 atom or a single trace of the energy represented in the primitive stock. 



These considerations also apply to all stimulatory actions, for although 

 the response may be altogether disproportionate to the stimulus, nevertheless 

 the latter represents a certain amount of energy, independently of whether 

 the exciting agent is a stimulatory substance or is physical in character. It 

 has already been mentioned that by the aid of the regulatory mechanism 

 gradual and continuous as well as sudden and transitory transformations of 

 energy may be produced, and that a local inhibition of a particular energetic 

 manifestation is possible. 



FFEFFBR. Ill 



1 Pfeffer, Studien zur Energetik, 1892, p. 163, 



Dd 



