and Laboratory Methods. 2045 



METHODS IN PLANT PHYSIOLOGY. 



V. 



IV. ROOT HAIRS. 



(a) Plant seeds of white mustard {Sinapis alba) or of buckwheat {Fagopynun 

 esculentum) in a crock of sand, allowing water to stand constantly in the saucer 

 beneath the crock. As soon as the seedlings appear above the surface loosen 

 the sand with a knife-blade and withdraw the seedlings. Observe how the par- 

 ticles of sand are held by the root-hairs. {l>) Germinate some pop-corn seeds 

 in damp sawdust, when they have attained a length of 3 or 4 cm. set up three 

 or four seedlings in a damp chamber and a like number in a jar with their roots 

 immersed in water. After two or three days observe the seedlings for the pres- 

 ence of root-hairs, noting their absence from the roots in water. 



V. PHYSICAL OSMOSIS AND IMBIBITION. 



1. A Convenient Osmometer. Slip a short piece of rubber tubing over the 

 small end of a thistle-tube and close the rubber tubing with a clamp. Fill the 

 thistle-tube with a 20 per cent, sugar solution and tie a piece of wet animal mem- 

 brane or parchment paper over the bowl of the tube. Invert the thistle-tube, 

 immersing the bowl in water, remove the piece of rubber tubing and mark the 

 height of the sugar solution in the tube, which should be about 2 cm. above the 

 bowl. If it is necessary to add more solution after the tube is inverted, use a fine 

 pointed pipette, allowing the solution to run down the sides of the tube in a 

 thin stream instead of drops. If air bubbles form in the tube they may be 

 broken up by inserting a fine wire. Support the tube with a clamp at such a 

 height that the liquid in the tube and the water outside are at the same level. 

 Record the rise of the solution in the tube every five hours. 



2. Artificial Cell. Smooth the ends of a short glass cylinder by grinding or 

 by fusion ; over one end tie firmly a piece of wet animal membrane or parch- 

 ment paper, fill the cylinder with a 20 per cent, sugar solution, and while the cyl- 

 inder is lying in a basin of sugar solution close the open end with another piece of 

 membrane, excluding the air. Place the cylinder in a dish of water for 24 hours, 

 then examine the membrane for a change in tenseness. If one of the mem- 

 branes is pricked with a needle and the needle quickly withdrawn, the spurting 

 of the liquid will indicate to some extent the amount of pressure. 



3. Traube's Cell. The osmotic action through a precipitation membrane is 

 well demonstrated by the familiar example of Traube's cell. Place a crystal of 

 copper acetate or copper chlorid in a small vial containing a 5 per cent, solution 

 of potassium ferrocyanide, immediately set the vial on the table and watch the 

 growth of the membrane of cupric ferrocyanide, which is at first globular then 

 cylindrical. 



4. The Rate of Diffusion. Slip a short piece of rubber tubing over the small 

 end of a thistle-tube, double the rubber tubing back upon itself and insert it into 

 a large test-tube nearly filled with water. Pour a few cubic centimeters of potas- 

 sium dichromate solution into the thistle-tube, by careful manipulation allow a 



