$26 LECTURE XIV. 



carbon dioxide and water exhaled in respiration, of oxygen 

 exhaled by green parts in sunlight, and of excreted organic 

 or inorganic matter, has been going on. Besides these items of 

 loss we must mention some others to which we have as yet 

 paid little attention. All plants lose a certain amount of matter 

 in connexion with reproduction, for all plants throw off from 

 themselves in the course of their lives, certain portions of 

 their structure, in the form of seeds, spores, antherozoids, etc., 

 for this purpose. Again, plants which persist for more than 

 one period of growth, lose matter by the falling off of certain 

 of their organs and of portions of their structure ; for ex- 

 ample, by the falling of the leaves in autumn, and by the 

 shedding of bark, fruits, etc. With reference to the expendi- 

 ture of energy, we have seen that a large proportion of the 

 income of energy is employed in the processes of constructive 

 metabolism and of nutrition, and remains stored up as poten- 

 tial energy in the organic matter which the plant accumu- 

 lates. A dissipation of energy in the form of heat and in 

 connexion with growth is common to all plants : in some, 

 there is dissipation of energy in the form of motion : in some, 

 in the form of light : in some, probably, in the form of elec- 

 tricity. A loss of energy, potential energy, occurs also when 

 the plant loses organic matter in any of the ways mentioned 

 above. We may now proceed to tabulate these various items. 

 They will be arranged under the two heads of (i) Income, and 

 (2) Expenditure. The water lost in transpiration is not con- 

 sidered, inasmuch as it simply traverses the plant : only that 

 amount of water is considered which may be assumed to 

 enter into the processes of constructive metabolism or to be 

 produced in the processes of destructive metabolism. 



PLANT POSSESSING CHLOROPHYLL. 



INCOME. 



Matter. 

 Food. 



Inorganic salts. 

 Carbon dioxide. 

 Water. 

 Free oxygen. 



EXPENDITURE. 



Matter. 



Organic matter. 

 Carbon dioxide ) 

 Water [Respiration. 



Free oxygen--- in decomposition 

 of CO 2 in light. 



