40 PLANT PHYSIOLOGY. 



glass-scale thermometers) make good graduates if wired to the liquid- 

 tube, or a wooden mm. measure may be wired firmly to the tube. 



To Graduate a Tube Permanently. Make the needed marks with a 

 fine file, and rub white lead into them ; or plaster of Paris containing 

 some insoluble color (as carmine) may be thus used. 



To Start a Siphon. Use a rubber tube, and immerse it in the liquid, 

 allowing it to fill ; pinch together one end so the air cannot enter, and 

 lift this end out over the edge of the vessel and let it fall below the inner 

 level ; let the pinched end open, w r hen the flow will start. Or fill a glass 

 siphon, and hold the fingers over the two ends until it is in position. 



To Make a U 7 ater-tight Joint betweeti a Glass Tube and a Cut Plant. 

 If the outer diameter of tube and plant is the same, slip a piece an inch 

 long of soft rubber tubing of somewhat smaller diameter over both; it 

 may be well (but not necessary) to tie the tube to the plant with a 

 stretched rubber band, and to tie it to the glass tube in the same way, or 

 with wire. If tube and plant are of different diameters, place upon the 

 smaller a half-inch of soft rubber tubing of a size proper to make it 

 nearly the diameter of the other; then slip a one-inch piece over them 

 both as above described. When relative size of plant and tube permit it, 

 it is well to fit a thin rubber tube over the plant, letting it project about 

 3 mm., and then push the tube over it so the plant and rubber fit like 

 a cork. Sometimes it is convenient to use a wax or cement instead of 

 the above joint. For this Detmer recommends a compound of 2 parts 

 olive oil, i part mutton suet and i part wax, the proportions being varied 

 somewhat according to w r eather, more oil being used at lower tempera- 

 tures. Tire-tape alone often makes a good joint. 



To Alake a Water- and Pressure-tight "Joint between a Cut Stein and 

 a Glass Tube. Prepare a water-tight joint precisely as described in the 

 preceding; then wind it tightly and carefully with several (4 or 5) turns 

 of electrician's tape or tire-tape. A stout rubber stopper makes a good 

 joint tight to moderate pressures. 



To Tie Joints, etc. In all cases where pressure does not matter, as in 

 fastening rubber to glass tubes, copper wire twisted tight by tweezers is 

 best. A single turn of the wire, with the ends pulled out by pliers until 

 the wire sinks all around into the rubber and then twisted tw r ice, makes 

 the best joint. Where pressure must not be too great the copper wire 

 is unsafe, and thread must be used, or, better, stretched rubber bands 

 which may be tied like string. 



To Make Small Joints, Stop-cocks, etc., Air-tig Jit. Where rubber tub- 

 ing wired on is impracticable, a cement may be used composed of a mix- 

 ture of vaseline and beeswax, a larger proportion of the latter being used 

 for higher temperatures. 



To Make a Tight Joint between Glass Tubing of Different Sizes. 

 Draw out the end of the smaller piece so that it tapers somewhat ; on 



