CH. V] TENSIONS OF TISSUES. 121 



is turned upside down and the root (which projects 

 vertically upwards) is covered with soft gypsum. A piece 

 of waxed paper in which a hole has been made (with a 

 hot needle) is slipped over the tip of the root and pressed 

 down with a bored glass plate. In this way the block of 

 gypsum a is formed ; when it is suflficiently set, the waxed 

 paper is removed, and for it is substituted a piece of wet 

 silk-paper on which the block b is added. The form of 

 the blocks a and b is regulated by cylinders of paper 

 acting as moulds. When block b is set hard it may be 

 removed from the root and trimmed with a knife : at the 

 same time the silk-paper may be removed. Before the 

 flower-pot is placed in the supporting ring m the block of 

 gypsum b must be secured in its place by tying it with a 

 thread which will be cut when the arrangement is 

 complete. The block b is fixed by fluid gypsum to the 

 glass plate c which rests on the spring/ 



The plate I, forming part of the spring, is fixed by the 

 small screws k, k to the solid plate g, which can be raised 

 and lowered by means of the screws h, h, h. In this way 

 the desired amount of pressure can be applied at the 

 beginning of the experiment. The distance between the 

 needle points is regulated by the screw i which moves the 

 lower needle. 



Section C. Tensions of tissues. 



(153) Longitvdinal tensions. 



The fundamental experiment illustrating the condition 



