4 BULLETIN 1339, U. S. DEPARTMENT OF AGRICULTURE 



relative value of the influencing factors; certainly none based on a 

 mathematical determination of their relative importance. 



Kenyon (21) and Kenoyer (20) called attention to Dufour's work 

 in the hope that others would carry on similar experiments, but no 

 extensive research seems to have been undertaken until the present 

 work. Discussions of factors influencing nectar secretion alone are 

 often somewhat misleading to the beekeeper, because factors which 

 may stimulate or retard nectar secretion may not be apparent at 

 the hive as shown by changes in weight or in the honey crop. 



Considerable work has been done on the problem of nectar secre- 

 tion and the influence upon it of temperature, humidity, altitude, 

 latitude, and similar factors, but little is on record other than casual 

 observations by beekeepers as to the influence of these factors on bee 

 behavior during the active season, either in or out of the hive. The 

 works on nectar secretion by Bonnier, Behrens, deLayens, and Ken- 

 oyer stand out prominently in this line. These writers and others 

 have made important contributions on the mechanism of nectar 

 secretion and on the factors influencing it. Unfortunately, only a 

 comparatively few plants have been studied for nectar secretion from 

 a physiological point of view, and when thus studied the number of 

 individuals of a species has of necessity been small. Too often obser- 

 vations have been confined to flowers cut from the plant in order to 

 control the governing factors, such as temperature and humidity, 

 thus leading to erroneous conclusions. Loftfield (22, p. 101) has 

 pointed out in the study of stomatal movement the great difference 

 in behavior between cut stems and potted or field plants of the same 

 species. 



It is quite evident that the factors influencing nectar secretion are 

 not necessarily synonymous with those affecting the changes in 

 weight of a colony of bees during the honey flow. In glancing over 

 papers dealing with nectar secretion there is usually no clear dis- 

 tinction drawn between the amount of nectar secreted and the sur- 

 plus honey gathered by bees, and one might assume that what affects 

 one should affect the other in like manner. This appears not to be 

 the case, as indicated by the data at hand. It is also evident that 

 data on nectar secretion for certain species of plants should be limited 

 largely to the species in question and not used for comparison with 

 other species in other localities. If climatic conditions affect the 

 behavior of bees in the same manner as they affect nectar secretion, 

 one would expect to find a close correlation between factors reputed 

 to be favorable both to nectar secretion and to increases in the 

 weight of colonies of bees, but such a correlation does not seem to 

 exist. It seems, therefore, either that the proper combination of 

 factors influencing nectar secretion has not been discovered, or that 

 the effect of weather conditions upon the behavior of bees is entirely 

 different from their effect upon plants. It has previously been im- 

 possible to determine by judging from the changes in the weight of 

 a colony of bees whether weather conditions influence the more 

 greatly bee behavior or nectar secretion; and, from the standpoint of 

 the practical beekeeper, the influence of weather upon colony weight 

 is far more important than its influence upon either nectar secretion 

 or bee behavior alone. 



