204 Effect of Temperature' and Insolation upon Growth 



to avoid any overshadowing. Maximum and minimum thermometers 

 were placed in several of the bottles and readings taken daily, and the 

 nutrient solutions were changed frequently. Two experiments were 

 carried through: 



(1) In spring, during the most favourable period for growth under 

 greenhouse conditions; 



(2) In summer, during the time that premature death of the plants 

 usually occurs. 



(1) Spring Experiment. 



Sutton's Harbinger Peas — April 18th to June 16th. 

 Growth proceeded satisfactorily with all the plants, and for some time 

 little difference was manifest; eventually the plants on the table began 

 to draw slightly ahead of those in the tanks, and they came into flower 

 somewhat earlier. When cut most of the plants showed incipient signs 

 of dying, as the upper leaves were turning yellow, indicating completion 

 of growth, but comparatively little difference was noticeable between the 

 two sets. The meaii dry weights proved to be 



The mean weekly temperatures (Fig. 1) show a difference of about 

 8-11° C. between the maximum of table and tank, and 3-5-5° C. 

 between the minima. In all cases the tank maxima were below those of 

 the table, and the minima above, as the surrounding water prevented 

 extreme fluctuations in either direction. On the table the mean maxima 

 ranged 15-5-22° C. above the minima, whereas in the tank the difference 

 was only 3-5° C. Nevertheless, in spite of these considerable differences 

 in root temperature, both as regards the actual temperature reached and 

 the daily fluctuations between maximum and minimum, the growth of 

 the plants was much less affected than might have been anticipated, 

 those on the table being somewhat the heavier. The improvement in the 

 latter case may be attributable to the higher average mean temperatures 

 prevailing throughout the experiment, while it was also probably in- 

 fluenced by the rather low temperatures at the beginning, when the 

 warmer conditions on the table gave the plants the advantage of a better 

 start by enabling them to grow more rapidly at first. This early start was 

 very important, as by the working of the compound interest law it gave 

 these plants a lead which those in the tank were never able to overtake. 

 The ratio of shoot to root was the same in each set, within experimental 



