CH. v] nobbe's experiment. 105 



(135) Stipa : mechanism of the movement. 



The twisting power of the awn depends on the hygro- 

 scopic torsion of its individual cells. To show this it is 

 necessary to isolate some of the elements. Prepare 

 Schulze's macerating fluid by dissolving in 50 c.c. of nitric 

 acid, 1 grm. of potassium chlorate ; add to this half its 

 volume of water, and boil a ripe awn cut into two or three 

 pieces in a test tube half full of the diluted liquid. It is 

 best not to boil it too much ; as soon as the awn is clearly 

 beginning to disintegrate it must be removed, thoroughly 

 washed in water\ and teased out with needles. A small 

 portion is now dried on a glass slip over a flame and 

 examined under the microscope. Cells will be found 

 which are obviously twisted on their axes, and which at 

 once untwist when water is added. 



(136) Nobbe's experiments 



Take two stoppered bottles of about 400 c.c. capacity : 

 fit each with a rubber cork through which passes a narrow 

 graduated tube. Half fill bottle A with whole peas, and 

 place the same quantity of split peas in B. Fill both 

 bottles with water which has acquired the temperature of 

 the room, and take care to get rid of any air adhering to 

 the peas ; force in the corks firmly, and note the height of 

 the water column in each bottle. If the peas increase in 

 volume by the amount of the water absorbed, the level of 



1 Because the fumes of Schulze's fluid are bad for the lenses of 

 microscopes. 



^ Handbuch der Samenkunde, p. 126. 



