1914] on Plant-Autographs and their Revelations 



181 



of personal equation. In fulfilment of this, I spent several years in 

 perfecting various instruments bv which the plant attached to the 

 recording apparatus is automatically excited bv successive stimuli 

 which are absolutely constant. In answer to this it makes its own 

 responsive records, goes through its period of recovery, and embarks 

 on the same cycle over again, without assistance at any point from 

 the observer (Fig. 5). In this way the effect of changed external 

 condition is seen recorded in the script made by the plant itself. 



The Sleep of Plants. 



In studying the effect of a driven change in the external condition, 

 an assumption has to be made that during the time of experiment 

 there has been no spontaneous variation of excitability. Is the plant 





Fig. 6. — Eecord foe Twenty-Four Hours, Exhibiting Diurnal Vari- 

 ation OF Excitability (spring specimen). The displacements of 

 base-line are due to nyctitropic movements. 



equally excitable throughout day and night ? If not, is there any 

 particular period at which the excitability remains uniform ? Is 

 there again a different time during which the plant loses its sensi- 

 biUty — going, as it were, to sleep ? On these points no definite 

 information has been available. The fanciful name of sleep is often 

 given to the closure of leaflets of certain plants during darkness. 

 These movements are brought about by variation of turgor, and 

 have nothing whatever to do with true sleep : for similar closure of 

 leaflets takes place under the precisely opposite condition of strong 

 hght. 



In order to find out whether Mimosa exhil)its diurnal variations 



