30 DISEASE IN PLANTS. 



the living plant, by conversions of energy of 

 potential independent of and out of proportion to 

 the chemical energy available by decomposing 

 the substances concerned ; even the heat of respira- 

 tion may be superfluous here, for the plant may 

 absorb heat from without, and convert it into 

 work. 



Tensions often arise in the plant, and do work 

 expressed as movements e.g. the springing of 

 elastic Balsam fruits, stamens of Parietaria, etc. 



Osmotic energy not only results in enormous 

 pressures and tensions, but causes movements by 

 diffusion and diosmosis, and any given osmotic 

 substance which carries this energy with it is not 

 necessarily formed always in the same way in the 

 ^ell e.g. glucose ma}^ arise from starch, or from 

 carbon-dioxide, or from oil. 



Surface-energy is also expressed in the powerful 

 attractions for water exhibited in imbibition, swell- 

 ing, capillarity, absorption, surface tensions, etc. 



Transpiration induces relatively enormous dis- 

 turbances of equilibrium, and does work in moving 

 water quite independent of chemical energy. 



Again, what may be termed excretion-energy, 

 as expressed in the separation of a solid body 

 e.g. a crystal from a solution, may be for our 

 purposes regarded separately. Any change in the 

 condition of aggregation of a substance in the 

 plant may result in movements and the over- 

 coming of resistances. 



It will be evident from this short digression 

 and this is the point I wish to emphasise that in 



