400 SOURCES AND TRANSFORMATIONS OF PLANT-ENERGY 



animals and plants, but must acquire much greater intensity in an actively 

 vegetating bacterium than in a slowly growing animal. The respiratory 

 activity and the production of heat are in fact much greater in rapidly 

 growing Fungi and Bacteria even than in warm-blooded animals. The 

 luminescence of a few plants and animals, as well as the feeble production 

 of electricity, represent relatively little energy. As comp ared with ordinary 

 animals and Fungi, chlorophyllous plants and animals have the advantage 

 of being able to convert a portion of the radiant energy of the sun into- 

 potential chemical energy. 



Although vital activity is in the first instance based upon chemical 

 energy, nevertheless all the natural forms of energy may take part in one 

 or other of the detailed reactions in the plant. Since electrical currents da 

 actually circulate in plants, and since every current radiates magnetic lines 

 of force while the different constituents of the cell have varying magnetic 

 permeabilities, it is impossible to deny that even magnetic forces may take 

 part in certain vital phenomena, more especially where a directive or 

 sorting action is necessary. Thus the direction and maintenance of regular 

 streaming in a constant direction may involve some action dependent upon 

 the paramagnetic properties of the cell -wall and the varying magnetic 

 permeabilities of the remaining cell-contents 1 . In this connexion it is 

 interesting to notice that a constant direction of streaming is only main- 

 tained in cells provided with a cell-wall, or in cells containing a single 

 large central vacuole ; so that the streaming protoplasm is near to and 

 remains approximately equidistant from the cell-wall at all points. In 

 naked cells, and in cells crossed by strands of streaming protoplasm, the 

 direction of streaming is more or less variable and capable of reversal. 



Osmotic energy is of the utmost importance in plants, and is a form 

 of energy dependent upon the number of particles in unit volume and 

 their kinetic energy. It is, therefore, comparable with gaseous pressure, 

 and both osmotic pressure and gaseous pressure are related to diffusion, 

 since all three involve the existence of movement among the molecular or 

 ionic particles 2 . Surface-tension energy is involved in the phenomena of 

 capillarity, imbibition, swelling, and also absorption so far as no chemical 

 reaction takes place, for we may include under this form of energy all 

 energetic manifestations shown between solid and fluid bodies independ- 

 ently of whether these take place between visible or invisible and external 

 or internal component particles. 



The energy of crystallization or of precipitation may be used in 



1 Cf. Ewart, Protoplasmic Streaming in Plants, 1903, pp. 33, 45, 116. 



2 On the different forms of energy cf. Ostwald, Gnmdriss d. allgem. Chemie, 3. Aufl., 1899,. 

 p. 247; Lehrb. d. allgem. Chemie, 2. Aufl., 1893, Bd. II, Th. i, p. n. In regard to plants cf. 

 Pfeffer, Studien zur Energetik d. Pflanzen, 1892, p. 159, in which work the subject is discussed fully 

 for the first time. 



