11 



INTRODUCTION. 



time, they labour under certain disadvantages in the study of the physiology o! 

 tropical organisms. They cannot place 



the latter under strictly normal condit 



and are therefore constantly liable to 



um 



that 



phenomena which 



present 

 occurring 



The phenomena of movement occurring. in plants with their 



ditions can. 



themselves under unnatural conditions may be taken to represent those 

 under natural ones. 



roots cramped within pots and exposed to quite abnormal atmospheric coi 



in no sense, be taken as affording accurate indices to those occurring normally 



Had Sachs had any practical experience of tropical conditions, he could hardly have 



eriously 



tertained the idea that the power of movement possessed by the lea\ 



of 



Mimosa pudica has been evolved in connection with the protection which it provide 



against 



»M 



from hailstorms 





\ 



