6 THE SIGNS OF LIFE [LECT. 



on in an apparently dry and perfectly dormant seed ; and 

 secondly, it is possible that chemical change may be completely 

 and absolutely arrested (e.g., by low temperature) without that 

 arrest being of necessity final and definitive. 



I will place evidence before you of this first point, which I 

 have investigated at some length. As to the second, which I 

 have not myself investigated, I will only mention that it appears 

 to be established by the observations of Horace Brown,* who 

 found that dry seeds kept for no hours in closed vessels at a 

 temperature of -- 183 to 192, i.e., seeds in which the arrest of 

 chemical change must be considered to have been absolutely 

 complete, germinated quite normally when they were placed 

 under suitable conditions of temperature and moisture. 



The inadequacy of our chemical methods to reveal small or 

 infinitesimal chemical changes taking place in seeds is, I think, 

 proved in two ways. We know, in the first place, that kept 

 seeds \vear out, that the percentage of seeds that germinate and 

 grow is smaller and smaller with the number of years they have 

 been kept. The deterioration is more or less rapid according 

 to the nature of the seed and the character of its protective 

 coats, but in every known instance there is deterioration sooner 

 or later, and I think you must admit such deterioration to be 

 sign and proof that chemical change has taken place. f 



4. Seeds. A still closer and more manageable proof that 

 seeds may be the seat of chemical changes which chemical 

 methods are inadequate to reveal, is, as I shall develop in a 

 future lecture, afforded by an electrical method. As formally 

 laid clown above, electrical changes are the token of chemical 

 changes, which are the token of the living state. And these 

 electrical changes are manifested by seeds long before the 



* Proc. Roy. Soc., vol. Ixii., p. 160, 1897. Thiselton-Dyer has gone 

 further, viz., to - 250 to - 252, Proc. Roy. Soc., vol. Ixv., p. 361. 



+ The continued formation of aleurone granules in very old seeds is in 

 certain instances an objective sign of the occurrence of slow chemical 

 change. The germination of "mummy wheat" must be set down as 

 apocryphal, in spite of the wheat sheaf shown in a Paris museum grown 

 from Mariotte's mummy wheat. The wheat was given to Mariotte by 

 Arabs. 



