EFFECTS OF LIGHT AND TEMPERATURE ON PLANT GROWTH 



561 



called "purple" hereafter— has its main absorption in the range 4,800 

 to 5,650A.; No. 81, flame tint— light gray— and No. 80, neutral gray, ab- 

 sorb all wave lengths equally. ) 



In Figure 1 the growth rates of plants under different filters are 

 plotted as a function of time. It shows the comparative growth under a 

 pink and under a light gray filter, each passing about 70 per cent of the 

 total sunlight, and under a purple and a neutral gray filter each trans- 

 mitting about 40 per cent of the sunlight. It is obvious that growth be- 

 came progressively better when the green part of the spectrum was 

 filtered out of sunlight. This was reflected not only in the growth rates 

 but also in wet weight and in leaf size. 



For another experiment, carried out in the same way, the total 

 growth and wet weight were plotted as a function of the light intensity 

 (Figure 2). Again the results were the same: removal of the green rays 

 speeded up growth and the wet-weight production. 



These results may explain the inhibitory effect of the high-pressure 



15 



10 



o 

 •o 



E 

 E 



X 

 O 



o 



-green 



+ green 



•— + 



Total intensity 

 707o of daylight 



-green 



Total intensity 

 40% of daylight 



I 



2 -^ 



X 



O 



ijj 



6 LU 



15 



20 



25 DAYS 



Figure 1. The growth rates and final wet weights of tomato plants growing 

 under gray filters, which let green light pass (+ green), and under pink or 

 purple filters, which screen out green light (— green). The plants were 

 grown in sunlight, reduced by the filters to 70 per cent and to 40 per cent of 

 its normal intensity, and at a day temperature of 26° C. and night tempera- 

 ture of 20° C. 



