206 Effect of Temperatwre and Immolation upon Gn'owth 



error, showing that the variable temperature had not caused any change 

 in the development of the roots compared with that of the shoots. 



The daily average of sunshine over the whole period was seven hours. 

 During the first month the total hours per week were somewhat low, 

 but May 16th-23rd was a very sunny week, ten to fourteen hours being 

 registered on each of five days. After this no further period of excessive 

 sunshine was recorded. At first the temperatures fluctuated to some 

 degree with the amount of sunshine, bat later were independent of it, 

 for when the total sunshine dropped during the last five weeks, the mean 

 temperature remained very constant and high, 27-28-5° C. 



It would thus appear that under similar conditions of light and pro- 

 vided no inhibiting factor such as excessive insolation comes into play, 

 the amount of daily fluctuation of root temperature has comparatively 

 httle effect on the growth of peas within a total mean range of 7-29° C. 

 provided that the mean temperatures do not vary considerably. These 

 are ■ the limits in the experiment under consideration and possibly 

 might be extended to some degree in either direction. Within those 

 limits a large variation in maxima, up to 11° C, will permit of much the 

 same amount of growth as measured by dry weight, though a low mean 

 maximum (below 16° C.) in the early stages may cause some retardation. 

 Growth proceeds equally well whether the temperatures at the roots are 

 fairly even, varying within 5° C, or whether they fluctuate as much as 

 22° C, on the average, i.e. within certain limits high maximum tempera- 

 tures associated with low minima have the same ultimate effect on growth 

 as low maxima and high minima. 



(2) Summer Experiment. 

 Sutton's Harbinger Peas — June 24th to August 3rd. 

 The experiment was begun in hot sunny weather when temperatures 

 ruled very high and the number of hours of sunshine was excessive. 

 Very soon many of the unprotected plants on the table began to show 

 signs of distress, turning pale and wilting, and within eighteen days 

 many were dead. In six weeks there were only four survivors, and these 

 were small and distinctly unhappy. The plants in the tank grew well 

 from the beginning and remained green and healthy to the end, only one 

 faihng. At the time of cutting the upper leaves were just beginning to 

 turn yellow, showing growth was finished. The mean dry weights were: 



Ratio 

 Shoot Root Total shoot/root 



gm. gm. gm. 



Table (4 plants only) M57±09l ■214±-026 1-371±-109 5-63±-478 

 Tank (23 plants) l-839±-007 •227±-075 2066±-078 8-26i-289 



