200 TULIP, WARMTH. [CH. VIII 



from 7 to 12 mm. in length are closed at one end by 

 melting the glass, and are filled with the malic acid 

 solution with the help of an air-pump. The solution may 

 be either the free acid or a salt, for instance, sodium 

 malate ; the solutions should be made with rain water and 

 contain about 0'05 per cent.^ A capillary tube is pushed 

 under the cover-glass and the antherozoids in the 

 neighbourhood of the opening are at once attracted to it. 

 Pfeffer has seen 60 antherozoids enter a tube of malic acid 

 within half a minute from the beginning of the experiment. 



(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". 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 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. 



1 The strength may vary from O'Ol to O'S per cent. 



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



