28 RELATIONS OF PLANTS TO MECHANICAL FORCES 



42. Curvatures of Roots away from Solid Objects, Soak a 

 number of peas or beans for a day in water and then place in 

 moist chamber. When the roots are 2 cm. in length provide a 

 large bottle with a wide mouth and a cork stopper. Fasten the 

 seedlings to the under side of the stopper in such position that the 

 tips of the roots will be directed perpendicularly, when the stopper 

 is put in place. To attach the seedlings to the stopper bore a 

 hole in a small cork of sufficient size to enclose the main root, 



a 



FIG. 13. Leaf of Drosera. a, surface view of tentacle, b, parenchyma cells, f 

 epidermal cells from base of peduncle showing stomata. d, section of tentacle. ( From, 

 alcoholic material. After Belzung. ) 



holding it firmly, split it and place it around the root, fastening the 

 halves together , by means of pins driven through them. The 

 cork may now be pinned to the stopper. Pour a few cc. of water 

 into the bottle, and place in a room at 16 C. Cut squares of 

 cardboard or paper 1.5 by 1.5 mm. and attach to the slope of 

 the root-apex of half of the roots. These bits of paper should 

 be fastened to the root by being moistened with gum and water, 

 or shellac, in a position at right angles to the plane of the coty- 

 ledons. Note the resulting curvatures of the roots during two 

 or three days and compare with the form of the ones which have 

 not been treated. 



Set up the experiment as before but do not fasten objects to the 



