CH. VI, 5] METHODS OF CROSS-POLLINATION 



295 



to the economy of the plant as a whole, but also certain sup- 

 plementary functions essential to their own nutrition or 

 safety. Thus pollen is commonly liable to injury by water, 

 i.e. rain, through osmotic absorption, as earlier shown 

 (page 234) ; but many flowers are completely inverted, thus 

 shedding the rain, as in 

 Columbine (Fig. 207), or 

 the petals overarch the 

 stamens, or scales and 

 hairs prevent access of 

 raindrops, or other ar- 

 rangements occur. Also 

 the nectar is attractive 

 to insects too small, or 

 unadapted by habit, to 

 effect pollination, no- 

 tably ants, against which 

 there must needs be pro- 

 tection ; and a good many 

 corresponding adapta- 

 tions have been claimed 

 in flowers, the closed 

 throat of the Snapdragon, 

 which bees can open but 

 ants cannot, the adhesive 

 glands on the calyx of 

 Plumbago, the hairs in 



the throat of many flowers, FIG. 207. The Columbine, Aquilegia 

 -I i ,1 canadensis, showing the inverted position 



and a good many others, of the flowers (From Bailey } 

 for further accounts of 



which the student must turn to the special works. Of 

 course, as with other organs, various hereditary and struc- 

 tural factors also enter into tho construction of particular 

 flowers, which therefore can by no means be explained in 

 detail upon the basis of adaptation to insect-pollination 

 alone. 



