EFFECT OF POISONS 97 



taking in or using of oxygen in respiration. IMany 

 parasitic plants, e.g. bacteria and fungi secrete poisons 

 or induce activities in the cells of the host that lead to the 

 accumulation of poisons that may destroy the life of a 

 cell or lead it to abnormal growth or functioning. 



Laboratory Studies, (a) Take a piece of the root of a living 

 red beet. Cutout a cube a centimeter or so in diameter. Wash 

 off the colored cell sap that has escaped from the cut cells and 

 place the cube in a test tube of water. So long as the cells are 

 alive their plasma membranes prevent the colored solute in the 

 cell sap from escaping. Gently heat the test tube. When the 

 death point of the beet tissues is reached (below G0° C.) the 

 plasma membranes are no longer impermeable and the color 

 diffuses out into the surrounding water. This experiment also 

 shows that the cell walls themselves are but slight obstacles 

 to diffusion. Instead of by heating, similar results may be 

 obtained by using certain poisons such as strong alcohol, etc., 

 but care must be taken not to choose a substance that will 

 destroy the coloring matter. 



(b) Set up a series of water cultures as follows : Take glass 

 jars (]\Iason jars will do) and to keep the contents dark encase 

 each with a cylinder of pasteboard which can be removed to 

 permit of observation. Fill these jars nearly full of the solution 

 to be tested, leaving a small air space between the water and 

 the cork. The cork should have at the center a hole 5 or 

 6 mm. in diameter. Germinate some peas, corn, buckwheat or 

 mustard seeds. When the radicles are 2 to 3 cm. long, fasten 

 one seed to each cork in such a way that the root just enters the 

 solution and the plumule is in a position to pass uj) through the 

 hole in the cork (or the seed can be fastened outside with the 

 root passing through the hole). Instead of a cork the jars may 

 be nearly filled with water and melted parafhn poured upon it ; 

 after the paraffin has hardened several holes may be made 

 through it by means of a hot metal rod. The water can now 

 be poured out and the desired liquid poured in, nearly up to the 

 under side of the paraffm. The germinated seeds can be set 

 upon this paraffin cap in such a way that the radicles will pass 

 throu2;h the holes. Expose all the jars to the same light and 

 temperature so that as far as possible the only differences will 



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