178 THANSACTIONS AND PROCEEDINGS OF THE [Sess. lxvi. 



exhibits so high a degree of suggestibility. The child- 

 mind maintains for so short a time, and in so slight a 

 fashion, any one course of action or set purpose, that 

 almost any fresh idea (suggestion) from parent or play- 

 mate can divert it into a fresh channel, and the new- 

 idea, in turn, can be easily supplanted by some other 

 notion newer still. There is so little inertia of position 

 belonging to the idea in possession of the mind that the 

 idea can be very easily supplanted, and the new idea has 

 so little momentum that it can be at once turned out of its 

 course by some new thing. Thus a volatile nature is one 

 with but slight mental inertia of movement ; a " dogged " 

 temperament is one with much. The great obstinacy of 

 the uncultured, and the " fixed delusion " of the lunatic 

 are cases of excessively developed inertia of psychic rest. 

 Surely psychic anabolic inertia is responsible for the lack 

 of correspondence between sensation and stimulus as 

 formulated in the Weber-Fechne law ; certain increments 

 of stimulus not giving rise to any increase of sensation 

 until certain intensity-limits are passed. The insuscepti- 

 bility that exists through a whole series of increments of 

 stimulus, from the last sensation-producing increment to 

 the next one, seems one more instance of psychic inertia. 

 Lastly, the differences in duration of reaction-time (" per- 

 sonal equation ") between various kinds of people are 

 directly due to the differences in degree of the psychic 

 anabolic inertia of their cerebral cells. 



The graphic record of reaction-time gives us a measure 

 in fractions of a second of the degree of their cerebral 

 anabolic inertia, but their whole characters are a daily 

 and familiar exposition of psychic inertia of rest or of 

 activity respectively. 



The Latent Life of Plants. 



By E. A. Eobertson, M.A., B.Sc, r.E.S.E_ 



(Read 13tli February 1902.) 



The manifestation of plant life depends on certain 

 external conditions, and in reference to these it is usual 

 to make a distinction between the tonic and the stimulant 

 effects. That particular combination of influences necessary 



