10 GENERAL BIOLOGY 



See how the loosestrife flower is adapted to small pollen 

 eating bees. Its stamens stand erect with anthers curving 

 inward. The trough-like pollen cavities of the anthers, 

 opening upward, expose their stores to the insect standing 

 on the top. So great is the excess of pollen production over 

 actual needs that the little the bee wastefully and unwit- 

 tingly scatters over the stigma is enough for setting the 

 seed. This store of choice food the flower reserves for its 

 proper visitors chiefly for this little bee. Large bees 

 would have great difficulty in collecting pollen from flowers 

 that hang on such slender stalks. Wingless insects, like 

 ants, which, if gathering pollen, could run only from flower 

 to flower upon the same plant, and which would thus be 

 poor agents in cross-pollination, are rigidly excluded. Should 

 they be able to run out along the slender flower stalk, and 

 round the fringed border of the corolla and get inside it, they 

 would still find between themselves and the pollen overhead 

 a barrier of glandular hairs bearing an acrid and offensive se- 

 cretion with which they would choose to avoid contact. 

 This flower has a simple and very common device for 



preventing self pollin- 

 ation. Its anthers ma- 

 ture in advance of its 

 stigma. When the flower 

 opens the stigma is 

 turned aside (in the 



FIG. 4. Tfce flowers of a willow (Salix dis- '4-*.-, *^A + ^n4-nA "k-TT-4-V.Q 



color.) r, a single pistillate flower, removed pOSltlOn indicated by the 



from its cluster; x, its covering scale; A^4-4-*A M~me* +~* >rr *\ "k-n-t- 



n, nectary, 5, section of its ovule case; I, dotted llIlCS in tig. 3) , t>Ut 



clusters (catkins) of staminate flowers; ! + oiioTlir -nrhon i+c 



M, single staminate flowers removed from later, USUally Wnen ItS 



own pollen is removed. 



the stigma is lifted up into the proper position for receiving 

 that brought by some late visitor from another flower. 



This simple illustration of the more general phenomena 

 will serve to introduce the following studies of the subject . 



f/i 



