140 SPLIT STEMS. [CH. V 



lead wire of 8 10 grams) on the loop, and read off the 

 position of the index. Remove the weight, and bend the 

 shoot two or three times backwards and forwards in the 

 vertical plane. When the weight is once more attached, 

 the index will move through a greater distance than that 

 at first recorded. 



(162) Increased length. 



Since the pith is in a state of compression, any in- 

 creased length of the cortical tissue must result in an 

 increase in the length of the whole shoot. Therefore 

 bending a turgescent shoot backwards and forwards as in 

 experiment 161, must lengthen it. The length must be 

 accurately measured, say to O'l mm., to make sure of a 

 result. 



(163) Splitting turgescent tissues. 



The relation between the compressed pith and the 

 stretched cortex can be demonstrated by dividing a shoot 

 longitudinally. It is best to prepare the shoot by cutting 

 it flat on two opposite sides, making a slab of pith 

 bounded on two sides by strips of cortical tissue : this is 

 placed on a glass plate and bisected with a knife, when 

 each half curves so that the pith is on the convex, the 

 cortex on the concave side. The curvature can be greatly 

 increased by putting the half-shoots in water. This 

 increase is strikingly seen if a scape of dandelion (Tarax- 

 acum) is split into 4 or 5 longitudinal strips, which curl 

 up in water into spirals of many turns 1 . 



1 This fact has already been utilised in experiment 148, p. 126. 



