DESSICATION IN PLANTS. 157 



quite possible that a more or less marked dissociation of 

 the protoplasmic molecule into less complex substances 

 has taken place and the latent period may be the expression 

 of the time required for the completion of the necessary 

 re-combinative changes, the energy supplied by the forcible 

 re-absorption of water, affording the necessary stimulus. 

 Where there is no perceptible latent period the dissociative 

 changes have probably been only slight or absent, the 

 change to the dry condition involving merely a rearrange- 

 ment of the protoplasmic molecule. "Where actual dis- 

 sociation takes place, the less complex substances, one of 

 which may be water in a combined form, into which the 

 protoplasmic molecule is resolved, do not necessarily 

 separate from each other but may remain within the 

 spheres of attractive influence of their respective molecular 

 groups so long as vitality is retained, falling asunder and 

 losiug the power of re-combination when vitality is lost. 



Such dissociatory changes appear to take place when 

 the amount of water present approaches to the minimum 

 consistent with the preservation of vitality, and are hence 

 produced by prolonged dessication or dry heat,* but they 

 may occur even when the amount of water present is 

 considerably over 10% of the dry weight, viz., in Lichens 

 or Mosses kept air dry for long periods of time, and 

 normally in seeds on ripening and drying as instanced by 

 the latent period of respiration shown by moistened 

 seeds, f 



Assuming the correctness of the above deductions, very 

 plausible explanations can be offered of most of the 

 phenomena observed in this connection. The " inhibitory 

 after effect " is explained as being really a latent period of 

 recovery. It is possible also to understand, in this light, 



* Journal of the Linnean Society, 1896, p. 373—377. 



t On Vitality of Seeds. Trans. L'pool Biol. Soc, Vol. VIII., 1894, p. 234. 



