Arrangements for Securing Union of Sexes 321 



Alpine plants in particular are famous for their beautiful colora- 

 tion. An explanation thereof has been found in adaptation to the 

 comparative scarcity of insects in these places, the extra brilliancy 

 representing the extra difficulty of ensuring their visits. Again, 

 a good many flowers exhibit a considerable variegation of color, 

 consisting chiefly of definite spots or lines quite different in hue 

 from the ground color of the flower as a whole, as Forget-me-nots 

 and Nasturtiums well illustrate. But these markings are found 

 always to have one feature in common, that they indicate the 

 position of the nectar. The floral color as a whole brings the 

 insect to the flower from a distance, and these markings then show 

 it the place to probe for the nectar, which of course brings it 

 into the position where it can best leave its pollen and receive an 

 additional supply. Again, the effectiveness of color is obviously 

 increased by massing, which explains the value of clusters of 

 flowers, especially for kinds that are small. Finally, as to this 

 matter of color, we need note but one more peculiarity. Some 

 kinds of flowers, though none that are very familiar, change color 

 immediately after fertilization; and it is claimed that such flowers 

 are no more entered by insects, whose visits would obviously be 

 useless to both the flowers and themselves. The same end is here 

 attained, though by a different method, as in the case of the 

 drooping flowers of the Aristolochia already described. The ad- 

 vantage to the species as a whole of preventing useless visits of 

 insects, and thereby conserving then- services for flowers which 

 still need them, is sufficiently obvious. 



As an advertisement to insects of the position of the flower, 

 color often is aided, and sometimes replaced, by odor. It has 

 even been claimed in late years that insects are guided to flowers 

 much more by odors than colors, many of such odors being hardly, 

 or not at all, perceptible by us; but the evidence on this point has 

 not yet won acceptance. However, there is no question at all as 

 to the assistance rendered by odor to color in those cases where 

 color alone cannot be made sufficiently conspicuous. This is true 



