INFLUENCE OF WATER 131 



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 consequently heating, 

 of stored seeds is great. It is not unlikely that the respira- 

 tion 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.* 



Jacquot and Mayer f observed the respiration of the dried 

 seeds of the bean, maize, etc., and found that, as in plants 

 periodically subject to desiccation (see below), respiration 

 progressively increases with the increase in the amount of 

 water to a maximum which is characteristic of the plant. 

 A further increase of water leads to a diminution of the 

 respiratory rate. They consider that the intensity of res- 

 piration depends not only on the contents, including water, 

 of the cell, but also on their relative properties. Bailey 

 and Gurjar $ find that the spontaneous heating of damp grain 

 when bulked 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 produce a 

 marked respiratory acceleration. In this respect glutenous 

 material is important in that its degree of viscosity is lowered 

 as it takes up water ; this permits a more rapid diffusion and 

 hence a greater respiration. This is illustrated by the fact 

 that soft starchy varieties of wheat exhibit a higher respira- 

 tion intensity than hard vitreous wheats with the same per- 

 centage of water. The embryo is the seat of enzyme secretion ; 

 shrivelled wheat, which contains less endosperm and the same 

 amount of embryo as compared with plump wheat, shows a 

 respiratory activity twice or thrice as much as plump with the 



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

 t Jacquot and Mayer: "Ann. physiol. physichim. biol.," 1926, 2, 

 40S. 



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



9* 



