14 EFFECTS OF ARTIFICIAL SHADING ON" PLANT GROWTH. 



During the period of experimentation the rainfall was in excess of 

 21 inches and the problem of water supply was never of importance. 

 Under all shades the soil was constantly in a moist condition, the 

 samples taken for moisture determinations showing no differences of 

 importance to plants. The soil was well drained. 



In bed A the influence of the different shades was independent of 

 their effects upon temperature and humidity, since these factors 

 were neutralized by the use of the fan. Wind movement due to the 

 fan was only slight, the movement having been less than 1 mile per 

 hour in section 1 and entirely negligible in sections 3 to 6. In bed B 

 the results under the different shades may have been influenced by 

 the accompanying changes in temperature and humidity. 



EFFECT OF DIFFERENT LIGHT INTENSITIES ON PLANTS. 



MUSTARD. 



In section 1 (n/93) the plants of mustard were unable to continue 

 growth after the reserve food material in the seeds was exhausted. 

 The light was too weak to enable the plant to elaborate carbohy- 

 drates. Growth ceased after about 25 days and the plants disap- 

 peared at the end of 30 days. 



At the end of 30 days (Table IV), when the plants in section 1 

 (n/93) had died, no great reduction in growth was observable in the 

 other sections with the exception of section 2 (n/15). In average 

 height the plants (Table V) were comparatively uniform under the 

 lighter shades at the end of 30 days. The diameter of stem (Table 

 VI) varied considerably, being smallest in section 2 and much greater 

 in the lighter shades. The stem diameter was not greatly increased 

 in full light. In fact, while in bed A the stems in full light were 

 slightly thicker than those under the shades, in bed B the stems 

 showed considerably less diameter in the full light than in sections 4 

 and 5. 



The general appearance of the plants at the end of 24 days is well 

 illustrated in Plate II, figure 3. Growth in full light and in sections 

 3, 4, and 5 was approximately the same. In section 2 the plants were 

 much dwarf ed,while no plants were able to survive in section 1. No 

 appreciable difference in the plants in beds A and B could be attrib- 

 uted to the air current of the fan and the resulting equalization of 

 conditions of temperature and humidity under the different shades. 

 Differences in light above one-seventh normal (n/7) seem to have had 

 very little effect upon this plant. 



At the end of the experiment, 51 days from the time of planting, 

 'the mustard plants showed the best growth between sections 4 

 and 5, or at light intensities between n/2 and n/5. When light 



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