EFFECT OF DIFFERENT LIGHT INTENSITIES ON PLANTS. 



15 



wa3 reduced to n/15 or below no plants were able to survive. The 

 mustard plants suffered severely from parasitic fungi, and on this 

 account final weighing and measurements were omitted. 



LETTUCE. 



Lettuce was unable to elaborate any food material in section 1 and 

 the plants died as soon as the reserve food material in the seeds had 

 been consumed. In section 2 growth was barely possible and the 

 plants were thin and emaciated at the end of the experiment. Let- 

 tuce could not continue growth where the light was reduced to less 

 than n/15. In this respect it showed somewhat less shade tolerance 

 than the mustard. In light more intense than n/15 no great differ- 

 ence was noted in the weight, although the plants were uniformly 

 heavier in sections 3 to 5 than in normal light. (Table VIII.) In 

 height plants 30 days old (Table V), as well as those 50 days old (Table 



Fig. 7.— Relative sizes of lettuce plants 50 days after germination. The numbers correspond to those of 

 the shades and the letters indicate the two beds in the experiment. (Traced from photograph.) 



IX), were consistently taller in sections 3 and 4. The diameter of 

 stem after 30 days (Table VI) and after 50 days (Table X) was not 

 substantially increased in full light as compared with light reduced 

 as little as to n/7. The stems in n/15 light were greatly reduced in 

 diameter. 



In figure 7 the relative size of the plants at the end of 50 days 

 is shown. Xo consistent differences attributable to the differences 

 in temperature and humidity could be noted as between bed A 

 and bed B. In the deepest shade the plants died more quickly in 

 the bed with the fan than in the bed without, but aside from this no 

 other differences were noted. 



Lettuce could not endure a shade greater than n/15. The best 

 growth was made under the lighter shades. In full light the plants 

 were smaller than in n 2 and n/5 light. Growth was best along the 

 line between these two shades. In flavor only a slight change could 

 be noted between the plants receiving full light and those receiving 



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