70 Diseases of Greenhouse Crops 



illumination, growth was barely possible. The 

 plants in this case were emaciated and worthless. 

 It seems, therefore, evident that lettuce cannot stand 

 shading where the light is reduced to n/\$. The 

 greatest amount of gain is made by lettuce when 

 the intensity of the light ranges between n/7 and 

 n/5. At this point the stimulation is greater than 

 in those grown under normal light or even at n/l. 

 In full light lettuce plants are smaller than in n/'] 

 or «/5 light. In flavor, a very slight change only 

 may be noticed between plants grown under full 

 light and those receiving n/l light. However, un- 

 der «/5 illumination the strong taste seems to dis- 

 appear entirely. When the light is reduced to w/y 

 the flavor seems to improve even more. Moreover, 

 m this case the plants acquire the particular form of 

 growth required by the market more consistently 

 than do those that are produced in brighter light. 



Effect of Different Light Intensities on 

 Radish 



Young radish seedlings seem capable of standing 

 about 30 days under n/93 illumination. At the end 

 of that time, however, they die. In «/i5 light there 

 is almost no growth. The best gains seem to be 

 made under a light of «/2 or n/^- In this respect, 

 the shade tolerance of the radish is somewhat simi- 

 lar to lettuce. However, the effect of shade is not 

 noticeable in the flavor of the radish. 



From the above evidence it is apparent that plant 

 growth is assisted by shading, the degree of which 



