DEPARTMENT OF BOTANICAL RESEARCH. 



95 



Figure 5 gives the integration of a thermograph air-record covering 

 the duration of the experiment, together with the dates of the experi- 

 ment. The short interpolated curve is the integration of a thermo- 

 graph record made in the root cage between November 24 and 30, 

 when artificial heating was employed. 



Period when artificia 

 heat was used in the 

 root cage 



12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 5 6 

 NOVEMBER DECEMBER 



Fig. 5. — Daily growth of the roots of desert perennials. The growth of Prosopis velutina is indi- 

 cated by the continuous line (A), and that of Fouquieria splendens (B) and Opuntia versicolor 



(C) by broken lines, -.-.-and , respectively. Scale: 2.5 mm. ordinate equals 0.5 mm. 



growth. 



