248 EVOLUTION OF PLANTS 



although the flowers themselves are inconspicuous. 

 Many such cases occur in the Euphorbia family, one 

 of the most familiar being that of Poinsettia, a common 

 greenhouse shrub, having the flowers surrounded by 

 numerous large, brilliant red bracts. 



We have already seen that in the more specialized 

 types of flowers there is usually a reduction in the 

 number of parts, accompanied by a tendency to a coa- 

 lescence of the members of each series of floral leaves, 

 and this often results in the production of a funnel- 

 shaped or tubular corolla which has the nectar secreted 

 at the bottom of the flower, where it can be reached only 

 by insects having a tongue long enough to probe to the 

 bottom of the corolla. Much less frequently this tubu- 

 lar form of the flower is due to the cohesion of the 

 sepals alone, the petals remaining quite distinct, as we 

 see in some of the pink family, e.g. the carnation and 

 catchfly. A study of such tubular flowers shows that 

 they are, for the most part, pollinated through the agency 

 of butterflies and moths, although some smaller insects 

 may visit them for the pollen. 



The characteristic odors of so many flowers are also 

 lures for insects, and sometimes, as in the mignonette, 

 this is the only means of attracting attention, as the 

 flowers are very inconspicuous in color. Many white 

 flowers have a peculiarly strong scent, which is usually 

 most marked at night : indeed, some flowers are odorous 

 only at night. An examination of these pale, night- 

 scented flowers soon reveals the fact that they are espe- 

 cially adapted to attract night-flying insects, the white 

 or pale yellow color, and strong odor, making them more 

 readily found in the twilight, or even after it is quite 



