COMPRESSION, TWISTING AND BENDING 29 



roots. Pour a few cc. of water into the bottle and then fill it up 

 with fragments of rock or glass until the tips of the roots are 

 nearly in contact with them when the stopper is put in position. 

 Observe the behavior of the tips when they come in contact with 



Fig. 14. Showing section of tip of young tendril of Ampelopsis muralis, old ten- 

 dril of A. quinquefolia and partial cross-section of latter, a, epidermis (dividing). 

 i, sub-epidermis (dividing), c, cortical parenchyma (dividing), d, collenchyma. 

 After von Lengerkin. 



the objects in the bottle. Both demonstrations will arrive at more 

 decisive results if the preparation is kept in a dark chamber. This 

 negative reaction of curvature by the root in response to the con- 

 tact of a solid body is one which would prevent the tip from being 

 foi'ced against any solid body in the soil in such manner as to injure 

 the growing point. 



43. Compression, Stretching, Twisting and Bending. The action 

 of any mechanical force which tends to change the form of a pro- 

 toplast, or a tissue generally causes a response of morphologic 

 nature, or a rearrangement of the elements of the living cell. 

 The principal reactions consist in the determination of the direc- 

 tion of the walls formed in the division of cells which process 

 may be exaggerated or set up anew under the influence of pres- 



