

I I 



I 



191 7] KENOYER— NECTAR SECRETION 251 



volume of water to a counted or weighed quantity of the flowers, 

 shaking frequently for half an hour, then decanting. A similar 

 method was employed by Von Planta (27) and Bonnier (2). In 

 some of the flowers investigated, this treatment extracts some 

 sugar from the floral tissues, as shown by the appearance in the 

 solution of colors from the floral envelopes, hence it is of value 

 mainly for the comparison of flowers of the same species. Buck- 

 wheat, because of its rapid maturing, its value as a honey-producing 



source 



was employed in many of the experiments. 



Sugar determinations were made by reduction of Fehling's solu- 

 tion. The method found most practicable and employed for the 

 greater part of the work was based on that described by Schoorl 

 (24). A carefully measured amount (1 cc. for minute quantities of 

 sugar, 10 cc. of the material to be analyzed in a 1500c- Erlenmeyer 

 flask) was heated on an asbestos gauze over a flame so adjusted that 

 the liquid began to boil in just 2 minutes, and then was boiled for 

 2 minutes longer. To the contents of the flask after cooling to 

 6o° C. were added sulphuric acid and potassium iodide. The liber- 

 ated iodine, which corresponds to the unused copper sulphate, was 

 titrated against sodium thiosulphate. Sugar values were obtained 

 by the careful analysis of known quantities of sugar. This method 

 has the advantage of being both rapid and delicate enough to deter- 

 mine minute quantities of sugar with a probable error of not over 

 o.o4mg. Floral tissues, when not too bulky, could be analyzed 

 by the same method, the reagents being added directly to the 

 tissues after covering them with water. When tissues were more 

 bulky or when greater accuracy was required, extractions were 

 made with alcohol or water, and were purified by treatment with 

 neutral lead acetate. 



HUMIDITY 



It is a well known fact that any watery exudation from plants 

 accumulates when atmospheric humidity is high and evaporation 

 is thereby retarded. This can easily be demonstrated in connection 

 with bleeding from severed tissues or with guttation through water 

 stomata. Bonnier (i) states that nectar secretion corresponds 

 to guttation and that it varies inversely with the transpiration. 



