﻿Heat of Imbibition by Seeds. 



By George Macloskie. 



The explanation of the production of heat in germinating 

 seeds by destructive metabolism, with the production of carbon 

 dioxide, is only part of the case ; and fails at the initial step, where 

 the necessity is greatest. Nor will it suffice to supplement our expla- 

 nation by suggestions of rising temperature of the atmosphere or 

 of the soil ; for in some cases germination has occurred at low- 

 temperatures, even at the freezing point of the soil. 



A supplementary, or rather a preliminary source of warmth 

 may be found in the discovery by botanists of a physical law, 

 which though not much discussed by either botanists or physicists, 

 seems to have large application to problems that meet us in all 

 branches of investigation. Sachs informs us * that heat is set free 

 when water enters into organized, and, to a smaller extent, unor- 

 ganized bodies ; stating that according to Pfeffer this was first es- 

 tablished by Pouillet, and that in 1865 it was confirmed by Jungk 

 and himself. Nageli's experiment on this consisted of drying flour- 

 starch, so as to deprive it as far as possible of all water, and then 

 immersing some of it in an equal weight of distilled water, which 



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cates a pressure equal to 34.3 atmospheres; hence u.6°C. will 

 represent many hundreds of atmospheres. (In fact it would 

 represent more than 13,000 atmospheric pressures, an almost in- 

 credible estimate.) This calculation enters into Sachs' theory of 

 the ascent of water in stems of trees, because of the high pressure 

 with which it forces its way into fine tissues like the wood-cells : 

 and which he further illustrates by reference to the use of wedges 

 of wood for splitting granite, on the application of water so as to 

 swell them. He accounts for the phenomenon by supposing that 



* Lectures on the Physiology of Plants, tran S late~dby~Vines 210 * 

 t Theorie der Garung. Abhand. der Akad. Wissensch. ' Miinchen, 13 = ^ 

 1879. 



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