EFFECT OF ALTERNATION OF LIGHT AND DARKNESS 537 



time is thus ensured, and it is thus possible to obtain 

 characteristic curves of numbers of different species of 



Fig. 190.— The Nyctitropic Recorder with four writing levers. Tiie flower 

 pots are placed in a trough filled with water to a constant height. The iirst 

 two levers are shown in the figure to record movements of leaves, the third 

 to record movement of a horizontally laid shoot ; the fourth lever attached 

 to a difEerenlial thermometer, T, records diurnal variation of temperature. 



plants within the short period of a season. The quadruplex 

 recorder enables us also to obtain simultaneous records 

 under identical external condition of leaves of different age 

 of the same plant, or of leaves of three different species 

 of plant. I have for the last five years taken records of 



39 a 



