2 5 2 



BOTAXICAL GAZETTE 



[APRIL 



So far as the volume of nectar is concerned, I have found this 

 to be true in all the plants experimented upon with this end in 

 view. But there are two factors involved in nectar secretion, as 

 shown by Pfeffer (20), the exudation of water and that of sugar. 

 Haupt (10) has found that extrafloral nectaries begin secreting only 

 when humidity is relatively high, an observation which confirms 

 the theory that secretion is due to a decreased permeability caused 

 by increased turgor, but that after secretion begins increased air 

 moisture increases water secretion, the secretion of sugar remaining 

 constant. It is probable that this applies to nectaries in general. 



more 



times 



Ames 



humidity, the summer months of the former year being 

 dry and warm, while those of the latter year were exce 

 and cool. Hence comparisons of nectar washed from 

 given in table I, are of interest. 



' 



TABLE I 





Species 



1914 



Melilotus alba, flowers 



Medicago sativa, flowers 



Trifolium pratense, corollas. 



Number of 

 samples 

 analyzed 



6 



4 

 4 



Average mg. 

 sugar per gm. 



1915 



Number of 

 samples 

 analyzed 



Average mg. 

 sugar per gm 



2I 3 



3-64 



3 



3 



13 



0.65 

 0.80 



3 90 



It is seen that the wet season yields rather less sugar than the 



dry. 



may be stated further that bee visitors 



several times as abundant in 1 914 as in 191 5. I have found by 

 experiment that flowers of alfalfa grown in dry soil contain about 

 60 per cent more sugar than those grown in wet soil. 



Buckwheat flowers kept humid under a bell jar secreted much 

 more liquid than flowers exposed to the rather dry greenhouse air. 

 However, 12 comparative analyses of the nectar of each show 

 1.04 mg. sugar per 100 blossoms in the humid, and o. 08 me. sugar 



per 10 blossoms in the dry. 



remov 



74 mg. 



t 





