PHYSICAL CONDITIONS. 



13 



peracure. This difference in the relative evaporating power of the 

 air in the different sections of bed B was very largely equalized in 

 bed A as a result of the wind movement caused by the fan. Stand- 

 ardized porous cup evaporinieters somewhat similar to those devised 

 by Livingston (1906) showed increased evaporation as a direct result 

 of the increase in light (fig. 6), independent of the relative evaporating 

 power of the air. It is also interesting to note that the increased 

 evaporation from the porous cup in the sections under the deeper 

 shades is due hi bed A to the wind movement and in bed B to the 

 higher temperature, while the increased evaporation in section 6 in 

 both beds was due to a third factor — increase in intensity of illumi- 

 nation. 



SUMMARY OF PHYSICAL CONDITIONS. 



In regard to light, both beds A and B offered exactly the same range 

 of conditions. In the two months during which the experiments were 



BED A BED B 



24 

 12 

















































































123456123456 



Fig. 6.— Diagram; showing the relative evaporation (in grams per day) from a porous cup for the entire 



period of the experiments. 



conducted there was approximately 70 per cent of possible sunshine 

 at the nearest station where observations were recorded. 



The results show that a slight reduction in illumination is accom- 

 panied by increased growth. In the lighter shades the occurrence of 

 dark days would reverse the conditions between such shades and full 

 light by reducing the light of the shades below the optimum, thus 

 overcoming to some extent the increase in growth of plants in these 

 shades as compared with those in full light : but in the denser shades 

 dark days would entirely stop growth, thus increasing the differences 

 in growth between the denser shades and full light or the lighter 

 shades. The illumination as shown by the recorded sunshine was 

 fairly normal or. if anything, above the normal for this locality 

 during the period of these experiments. 



In bed A the use of the electric fan during the day to provide a 

 current of ah- prevented entirely the changes in conditions of air tem- 

 perature and humidity which otherwise result when shade is applied. 

 In bed B all of the effects upon temperature and humidity resulting 

 from altered light conditions were operative. 



279 



