250 PLANT PHYSIOLOGY 



STERILIZING. Best done by steam in a suitable instrument. See 

 page 48. 



STOP-COCKS. Should always have their cores attached by string 

 to their tubes, as otherwise they are liable to fall and break. They should 

 be kept thinly lubricated by a special wax supplied for the purpose. 



TRANSPORTING EXPERIMENTS for demonstration purposes. 

 For this purpose the experiment should be set up on a tray (or a large indurated 

 fiber saucer) provided with handles. For this purpose I have devised a spe- 

 cial portable support or clamp stand, which is shown in figures 62, 63, and 

 is supplied among my normal apparatus. It proves very convenient in use. 



VACUUM. This, or an approach to it, may readily be made evident 

 in a small chamber by use of a small U-shaped tube of glass tubing sealed at 

 the end of one arm which is filled with mercury, the other arm being open 

 and only partly filled; a vacuum is marked by the fall of the mercury to the 

 same level in both arms. 



WAXES. Needed for making tight connections and some other uses. 

 A very excellent kind is a mixture of beeswax and vaseline, the proportions 

 being varied according to weather or use. It is well to have vials of various 

 combinations always ready. For some purposes cocoa-butter, which melts 

 at about 33 , is valuable (see page 166). 



WILTING. May be checked by method given on page 169. 



