CH. VIIl] TULIP, WARMTH. 201 



The filaments, each of which projects 3 cm. beyond the 

 flower, serve as indices for noting the movements of the 

 segments. The simplest plan is to fix a millimeter scale 

 horizontally so that the distance between the points of 

 the indices can be read off. The tulip should be prepared 

 in a room free from sunshine, and where the temperature 

 is not above 1.5° C, — a temperature of 11° or 12° better 

 still. 



The flower having been left to itself for 15 minutes is 

 placed in a temperature of about 20° C. In 5 or 10 

 minutes a clear increase in the reading on the scale shows 

 that the flower is opening. 



It may now be replaced in a temperature of 10° — 12° C. 

 Notice that the flower continues to open for some time 

 and then begins to close. The same phenomenon mutatis 

 mutandis is to be seen on changing a low into a high 

 temperature. It is easy to make a tulip open, close, and 

 open again within one hour. 



(251) Tulip: sensitiveness to small change of tem- 

 perature. 



Pfeffer^ has seen a crocus flower open slightly in 

 15 minutes during which the temperature rose by less 

 than 1° C. The change of temperature was produced by 

 opening the door between a cold and a warm room. For 

 elass-work it is perhaps best to try rather larger changes 

 of temperature. A tulip, fitted with two indices as 

 described above, shows distinct opening in half-an-hour 

 when moved firom a temperature of 13'5C. to a temperature 



' Physiologische Untermchungen, p. 183. 



