36 BULLETIN 1339, U. S. DEPARTMENT OF AGRICTJLTUJitf 



The writer found a correlation coefficient of —.3806 ±.0935 be- 

 tween change in the colony weight and diurnal relative humidity for 

 the spring period. In making a temperature correlation by means 

 of the same formula, he found T r<m= — .4058. In this particular 

 instance, it appears that dry atmosphere has a beneficial effect upon 

 the change in colony weight. 



The fall period showed less, or practically no, correlation between 

 changes of colony weight and diurnal average relative humidity, the- 

 correlation being -.0960±. 1240. 



It is interesting to note from Tables 2 and 5 that a wide variation 

 of diurnal relative humidity has a beneficial effect upon change of 

 colony weight, and that the coefficients of correlation in this case are 

 higher than those with the diurnal average relative humidity. 



The condition of the diurnal or nocturnal relative humidity of 

 the day preceding has practically no effect upon change of colony 

 weight. 



RELATIVE HUMIDITY AND MIDDAY DECLINE 



Figures 7, 8, and 10 show that the average minimum relative 

 humidity is reached previous to the average low point of the midday 

 decline. This fact, together with the existence of a negative corre- 

 lation between net gain and diurnal relative humidity, makes it dif- 

 ficult to assign low relative humidity as the cause for the midday 

 decline. 



RELATIVE HUMIDITY AND NOCTURNAL LOSS 



During the spring period the nocturnal relative humidity plays a 

 small part in the nocturnal loss. The coefficients for both the aver- 

 age and the variation in relative humidity are small and have large 

 probable errors. 



For the fall figures these factors are more important. The coeffi- 

 cient of —.4821 ±.0961 for the average nocturnal relative humidity 

 with nocturnal loss signifies that the drier it is at night the more the* 

 colony loses in weight. The greater the variation in relative humid- 

 ity during a night, the greater the loss, as is shown by the coefficient 

 of correlation of .5391 ±.0888. Thus it is seen that variation in rel- 

 ative humidity plays a more important part than the average relative 

 humidity upon nocturnal changes in colony weight. 



SOLAR RADIATION AND SUNSHINE 



It is a well known fact that both solar radiation and sunshine exert 

 a profound influence upon animal and plant life; it is therefore not 

 surprising to find that these two factors play an important r6le in 

 changes of colony weight. A number of investigators nave attempted 

 to learn the effect of light upon nectar secretion, but, as in other 

 experiments upon nectar secretion, various species of plants have 

 been used with the result that authorities differ in their conclusions. 



Ono {26) placed Ligustrum lucidium, Viburnum japonicum, V. opu- 

 lus, Prunus yedoensis, and P. laurocerasus in a dark moist chamber 

 and found that their young extrafloral nectaries produced no nectar 

 at all, but that their fully developed nectaries secreted in the dark 

 equally as well as in the sunlight. In the case of P. laurocerasus this 

 plant continued to secrete nectar in ample quantities for three weeks 

 while placed in a dark chamber, the nectaries being washed daily. 



