CH. V] ELASTICITY. 125 



carvi. If suitable material is wanting for following out 

 Detmer's instructions, it is generally possible to find roots 

 in which shortening has already occurred, and which are 

 remarkable for their wrinkled exterior. The roots of 

 hyacinths grown in water show the phenomenon well. 



(158) Imperfect elasticity of plant-tissues. 



The fact that the tissues of a growing shoot or leaf are 

 extensible, but not perfectly elastic, can be demonstrated 

 on a variety of material, e.g. a flower scape of Polyanthus, 

 or the leaf of a Narcissus: the form of the last named 

 makes it convenient for the purpose. For this and 

 similar experiments a strong sheet of cork mounted on a 

 board is convenient: one end of the leaf is clamped 

 between the mounted cork and a free block of cork, in 

 such a position that the other end of the leaf projects 

 beyond the board. Two marks about 100 mm. apart are 

 painted on the leaf, one being close to the clamped end. 

 The distance between the marks having been read on a 

 mm. scale, also clamped to the cork-board, the projecting 

 end of the leaf is pulled with the hand ; the distance 

 between the marks is now to be read off without releasing 

 the traction, and again when the leaf is left to itself The 

 leaf will be found to be permanently extended ; the tem- 

 porary and permanent extensions should be recorded in 

 percentages of the original length. 



(159) Cyclometer^. 



Take a straight turgescent shoot, e.g. a young cabbage 

 shoot, bend it forcibly, and then release it : it will be found 

 1 Sachs' Text-Book, p. 784. 



