304 VEGETABLE PHYSIOLOGY 



contain principally starch. Fungi which are fed with car- 

 bon-compounds that contain relatively little oxygen give 

 off relatively less carbon dioxide than others which are 

 supplied with food containing a large percentage of this 

 constituent. Organs which contain much protein matter 

 respire more copiously than others which contain but little. 

 The nature of the inorganic salts absorbed also influences 

 the process to a certain extent, though probably these only 

 -act indirectly. 



Eespiration is thus to be looked upon as a process very 

 largely connected with the utilisation of the store of energy 

 which each cell possesses, and to be perhaps primarily 

 concerned in the transformation of that energy from the 

 potential to the kinetic form. The oxygen appears to be 

 necessary mainly for the purpose of exciting those decom- 

 positions of the protoplasm which are so dependent upon 

 its instability. It is not, however, certain that this is the 

 only part it plays. It is possible that some of the products 

 of the protoplasmic disruption are oxidisable substances, 

 and that to a certain extent a direct oxidation of them takes 

 place. There is undoubtedly some evidence pointing in 

 that direction. 



We have, besides the true respiratory processes, a second 

 series of chemical decompositions going on in plants, pro- 

 bably in many cases closely allied to those of the first, if 

 not inseparable from them, but differing in that the auto- 

 decomposition of protoplasm is not necessarily involved. 

 We have seen already that many processes of oxidation and 

 reduction are probably always taking place among the sub- 

 stances which are in solution in the water with which the 

 cytoplasm is saturated. Besides these, other changes take 

 place in which no oxidation is involved, and this whether 

 oxygen is present or not. If the access of oxygen to a 

 protoplast is interfered with, its normal respiration soon 

 ceases, but very frequently other changes supervene, involv- 

 ing decompositions of a different character, which yield, at 

 any rate for a time, the energy required for life. 



