1914] East and Glaser—Relation Between Flower Color and Insects 29 
Total number Total number Per cent. of 
Flower color. of flowers on of flowers flowers 
10 average plants. fertilized. fertilized. 
WVinitebeces Aces scorn 18,035 7,052 39.10 
bellows. ceo hos 26,686 4,836 18.12 
TRG | aah ae 14,165 2,154 15.21 
IRurplesesse ee-cei 9,721 1,628 16.74 
Ten average plants of each of the four colors—white, yellow, 
red and purple—were selected at random. The total number of 
flowers produced on each color type during the flowering season 
(July 15 to October 15) was determined by counting the places 
on the racemes where flowers had been. The number of capsules 
present was assumed to be the number of flowers fertilized, al- 
though this count is not as accurate as the first by reason of the 
accidental loss of capsules. Long experience with Nicotianas, 
however, leads us to believe that this error is small. 
The first point to be noted is the comparatively small percentage 
of cross-pollination by insects. Numerous experiments on artificial 
cross-pollination have shown that a very small amount of pollen 
causes normal development of the capsules, yet the yellow, red 
and purple types had only about 17 per cent. of their blossoms 
crossed. According to the table, the percentage of white flowers 
fertilized was more than twice as high as any of the colored types. 
The reason for this is obvious. From the beginning of the flower- 
ing period, about July 15, to the end period of summer heat, about 
September 15, the flowers opened at about 4 p. m. and remained 
open until about 7.30 a.m. During the last month of flowering, 
the weather was so cool that the flowers also were open throughout 
the day. Nearly two thirds of the fertilizations occurred during 
the last month as could be determined by the positions of the 
flowers on the racemes. Furthermore the percentage of fertiliza- 
tions on the white type during the last month was about the same as 
on the colored types. Roughly, one might say then that about 6 per 
cent. of the pollinations of the colored types were made by night- 
flyers (Sphingide, ete.), while during the same period these insects 
pollinated from 20 per cent. to 25 per cent. of the white type. In 
