CONTROLLED ENVIRONMENTAL CONDITIONS 



301 



Figure 121. Clydesdale oats grown at 78° F (26° C). Beginning at left: control; 

 6 hours extra light and 0.3 per cent COo; 6 hours extra light, normal CO2. Control house 

 enriched with scrubbed flue gas. All plants 45 days old from seed. 



As is well knowTi, winter wheat is greatly delayed in heading and finally 

 heads only sparsely if the imbibed grains or the plants in the rosette stage 

 are not subjected to a low temperature for a considerable period. Fig. 122 

 shows a few heads starting on Hybrid 128 after 66 days' growth from seed 

 in the 6 hours' extra illumination and extra CO2 and under continuous illu- 

 mination. Turkey Red wheat shows no heads when gro\\Ti under like condi- 

 tions for the same period. The ragweed is a short-day plant as shown in this 

 figure. The plants grown in the control house during the winter months 

 are in flower, while those grown with 6 hours' extra illumination have not 

 flowered, although the 6 hours' extra illumination' gave a marked increase in 

 volume of growth. The extra CO2 in addition to the 6 hours' extra illumina- 

 tion again adds markedly to the volume of growth. This makes clear why 

 people in the latitude of New York begin suffering from ragweed hayfever 

 in August; the day length at that time is right for inducing flowering of 

 the weed. An 18-hour day for the entire growing season would largely 

 eliminate flowering and ultimately destroy the plant, for it is an annual. 

 We have already mentioned that the tobacco plant is injured by continu- 

 ous illumination in the constant-condition room. This is illustrated in 

 Fig. 122. In this figure also it is evident that the tobacco plant shows great 

 additional gro^^'th in the greenhouse in winter when the sunlight is supple- 

 mented with 6 hours' artificial illumination at night. Extra CO2 in the air 

 together with 6 hours' extra illumination does not give additional grou-th. 



