10 



THE WATER-BALANCE OF SUCCULENT PLANTS. 



This is but an extreme case of variations which are frequently notice- 

 able. In this instance VI is probably in a position where there is great 

 flexibility of the parts, and it appears possible, from the fact that No. I 

 showed even less contraction than the other intervals on the plant, that 

 the strong- contraction at VI might have exerted a pull to keep the next 

 furrow spread open. At all events it is evident that in the movements 

 attending absorption and transpiration the plant does not act merely as a 



Mayl905| June 



20 30 27 



Fio 5.— Curves from two intervals on sahuaro No. 4. These represent an extreme case 

 of variation between two intervals located very close together. May 20 to October 

 23, 1905- 



mass of homogeneous tissue, but expands and contracts differently in very 

 localized regions, and that while these regions may, to some extent, be 

 classified according to their general position in the plant, this by no means 

 accounts for all the variations. When the furrows seem to have reached 

 the limits of their expansion during the rainy season the movement of 

 selected points was quite irregular and highly localized, as was illustrated 

 by the action of sahuaros Nos. 12 and 13, upon which intervals were taken 



