218 TULIP, WARMTH. [CH. VIII 



solution may also be used, of various strengths for 

 different plants 1 , e.g. Fritillaria imperialis, 15 p.c. ; 

 Narcissus Tazetta, 7 p.c. ; Vincetoxicum officinale, 15 p.c. 

 It should be noted 2 that all pollen tubes do not exhibit 

 this phenomenon. 



(250) Opening and closing of the tulip : temperature. 



Many flowers open with a rise of temperature and 

 close with a fall ; the best adapted for experiment are the 

 crocus and tulip 3 . Both of these are sensitive to slight 

 changes of temperature, and both are valuable because 

 they can be made by appropriate treatment to open and 

 shut at any time of the day. The crocus is the more sensi- 

 tive of the two, but the tulip answers extremely well, and 

 the following instructions apply to this genus. 



It is convenient to begin the experiment on a cool, 

 cloudy morning, when the tulips are naturally closed. 

 Cut a flower and fix it vertically in a cork fitted into a 

 bottle of water. To one of the outer perianth segments 

 and to the opposite inner segment fix filaments of glass 

 drawn out to very fine capillary tubes. They are best 

 cemented with shellac varnish to the groove or line run- 

 ning down the centre of the outer surface of the segment. 

 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 



1 See Molisch, loc. cit. , where a list of suitable solutions is given. 



2 See Molisch, loc. cit. 



3 Pfeffer, Physiologische Untersuchungen, 1873, p. 181. 



