Arrangements for Securing Union of Sexes 319 



on a plant and then visit only one on another, as would be theo- 

 retically the best of arrangements ; for on the one hand that were 

 too difficult a thing for the plant to be able to induce the insect 

 to do, and on the other it is needless. What happens in reality is 

 this, that an insect in visiting a plant usually goes successively to 

 all the flowers that are open, and thus becomes thoroughly dusted 

 all over by a mixture of pollen, which is ample in quantity to 

 allow some for each stigma of all of the flowers on the next plant 

 that it visits. Of course there is mixture of pollen, and a great 

 deal of pollination between different flowers on the same plant; 

 but the method makes probable the presence of some cross pollen 

 on each stigma, when the selective power of the stigma for cross 

 pollen, already mentioned, ensures cross fertilization. And the 

 matter is aided a good deal by a peculiarity of blossoming which 

 practically all plants show, that no large number of flowers are 

 open at one time in the same cluster, — no more, one may say, 

 than as many as an insect can polHnate by the quantity of pollen 

 it can carry on its body from a previously- visited plant. Of 

 course none of these arrangements are exact in their working, but 

 are general, or average, or clumsy, with many individual failures. 

 But on the whole they suffice. 



That insects find flowers chiefly through the colors seems un- 

 doubted, but there is more in the subject than appears at first 

 sight. The chief essential of floral color, from this point of view, 

 is conspicuousness, which of course involves contrast with the 

 background; and as this is commonly green, therefore white and 

 yellow and red are the commonest of floral colors, especially in 

 flowers that nestle among foliage. The less contrasted blue is 

 rather more common in flowers that stand out by themselves, 

 whether singly or in long terminal clusters. Furthermore, it is 

 true that some kinds or groups of insects show preference for 

 certain floral colors; and, correlatively, the flowers having such 

 colors are prevailingly of a size and construction better fitted to 

 the visits of those insects than of others. Thus, most small and 



