90 RESPIRATION 



behave alike in these respects ; the paeony and the asparagus 

 show no increase in respiration following removal of water, and 

 Palladin and Sheloumova* found that potato tubers exhibited 

 a lowering of respiration on dehydration under 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 is remarkable : 

 Long f found that a shoot of Echinocactus retained life and 

 exhibited respiration after a period of desiccation of thirty 

 months, the first eight in full sunshine and the remainder in a 

 dark room at air temperature. Seeds, however, provide the 

 most striking instances and the importance of a knowledge of 

 the conditions affecting respiration, and consequent heating, 

 of stored seeds is great. It is not unlikely that the respiration 

 of really dry seeds is, to a large extent, anaerobic ; in air-dry 

 seeds there is a small evolution of carbon dioxide which may 

 have its origin in the testa only.| With regard to the respira- 

 tion of bulked grain reference may be made to the results 

 obtained by Bailey and Gurjar. These authors find that the 

 spontaneous heating of damp grain is chiefly due to the activity 

 of the embryo in oxidizing sugars, the degree of respiration 

 increasing with the amount of available water. Up to 14*5 

 per cent of water there is a uniform and gradual rise in the 

 intensity of respiration ; in greater proportions, water will 



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



l-Long: "Bot. Gaz.," 1918, 65, 354. 



J Becquerel : "Ann. Sci. Nat. Bot.," 1907, 5, 193. 



Bailey and Gurjar: " Journ, Agric, Res.," 1918, 12, 685. 



