158 



Hydration and Growth. 



thickness are recognizable in changes in length, although the action 

 of 120 mm. of tissue is involved as against 2 or 3 mm. in the measure- 

 ments of thickness. The structural arrangement of the cell-masses 

 and the shape of the cavity of the pod would operate to minimize the 

 shrinkages so apparent when thickness is measured. 



i2p.m. m. 12p.m. m. 12p.m. m. 



FIG. 44. Tracing of an auxographic record of growth in thickness of pod of Phaseolus. Down- 

 ward movement of the pen denotes increase in thickness, X 45. Temperatures given are 

 of the air near plants. The sudden shrinkage between 5 and 6 p. m. took place during 

 a brief daily illumination by direct rays of sun. Scale ruled to 5 mm. and 12-hour inter- 

 vals. Summer-time schedule. (See fig. 40 for illustration of the arrangement of auxo- 

 graphic levers.) 



A pair of tests was now arranged in which one pod was placed in- 

 side a cell consisting of a short section of a glass T-tube of about 1 cm. 

 internal diameter. The pod was placed in a horizontal position in 

 the main section of this tube, which rested solidly on a concrete 



f WHMW \VVW\V 



FIG. 45. Glass chamber for controlling humidity in making auxographic record of pod of Pha- 

 seoliis. Ends of horizontal part of chamber closed by cork stoppers fitted to stem of pod 

 and thermometer. Tube to be closed around vertical arm of instrument with cotton wool. 



block. The end around its stem was closed loosely, and the opposite 

 end of the tube held a cork and small thermometer. The vertical 

 arm of the auxograph reached its bearing on the pod through the 

 upright arm of the T-tube and opportunity was given to keep record 



