130 RESPIRATION 



third to a half of the water had been removed, showed a greater 

 respiration as compared with normal members of the plants 

 mentioned. Up to a loss of 30 per cent, of water the respiratory 

 activity increased in proportion to the amount of water lost ; 

 from 30 to 60 per cent, loss of water the respiration was uniform 

 at the increased rate attained with the 30 per cent, loss ; finally, 

 with a loss of from 60 to 100 per cent, of water the respiration 

 decreased proportionately to the amount of water removed. 

 Iljin,* in a large number of observations on various plants, 

 both mesophytic and xerophytic, also observed that a loss 

 of water from the shoots stimulates respiration, which is 

 more considerable in mesophytes than in xerophytes. In the 

 latter plants, which from their habitat have a relatively low 

 reserve of food, the increase in respiration may cause a 20 

 per cent, depletion in the reserve food in the course of a day. 

 All plants do not behave alike in these respects ; the 

 paeony and the asparagus show no increase in respiration 

 following removal of water, and Palladin and Sheloumova f 

 found that potato tubers exhibited a lowering of respiration 

 on dehydration in the conditions of their experiments which 

 were not the parallels of those of the authors just quoted. 



There is no agreed explanation of these facts : Smith 

 suggests that the phenomenon is due to changes effected in 

 the activity of the enzymes involved, whilst Maige and Nicolas 

 consider that the increased turgescence increases growth 

 and consequently respiration whilst the decreased turgescence 

 stimulates respiration since the respirable materials are con- 

 centrated. If this be so, it is reasonable to suppose that there 

 is, mutatis mutandis, an optimal concentration of these sub- 

 stances, and it is the passing of this strength which accounts 

 for the diminution in respiration in tissues subjected to the 

 plasmolyzing action of strong sugar solutions. 



The long periods of time through which certain plants can 

 sustain life on a diminished water supply are remarkable : 

 Long % found that a shoot of Echinocactus retained life and 



* Iljin : " Flora," 1923, 16, 379. 



t Palladin and Sheloumova : " Bull. Acad. Sci. Petrograd," 1918, 801. 



% Long : " Bot. Gaz.," 191S, 65, 354. 



