156 GROWTH. [CH. VI 



tropic after-effect or for the movements of sleeping plants 

 (as described below) the drum described in exp. 181 must 

 be used. The following is a simple method of fitting up a 

 recording surface. Take a Bath-Oliver biscuit tin, or any 

 other sufficiently tall cylindrical box: pierce two holes 

 just below the point to which the cover overlaps : pass a 

 stout wire through the holes and support the wire so that 

 the box may hang with its long axis vertical and its lower 

 end close to the table. To the lower end fix a cork with 

 sealing-wax, and into the cork thrust vertically a strong 

 short pin. Take a cheap American clock and fix it to the 

 table in such a way that the axis on which the hand 

 moves is vertical, while the hand itself moves in a horizontal 

 plane. The clock is so placed that at each hour the hour- 

 hand just touches the pin fixed to the biscuit box and 

 causes the box to oscillate on the supporting wire. 



(183) Temperature: microscopic method. 



Select a bean root about 20 mm. in length, impale it 

 on a pin and fix it to the cover of a flat-sided plate-glass 1 

 vessel of water, so that the root is immersed and the hilum 

 just touches the surface. Having carefully levelled the 

 microscope, focus the tip of the root-cap, and note the tem- 

 perature of the water and the time of the observation. If 

 the root-cap is slimy and ragged it may be gently cleaned in 

 the fingers. The reading will gain considerably in sharp- 



1 A convenient arrangement is to use one of the rectangular glass 

 vessels used in museums and to cut out by the sand-blast a hole 40 mm. 

 long -by 25 wide on one side, which is afterwards closed by a large 

 cover-glass fixed inside with Canada balsam. In this way good defi- 

 nitions can be insured for the microscope. 



