120 PEACTICAL BOTANY 



Flowers of any other color than green, or which are fragrant, 

 have nectar, or show marked deviations from radial sym- 

 metry (Figs. 98 and 281), are generally more or less wholly 

 dependent upon animals (commonly insects of some kind) for 

 pollination. 1 



112. Wind-pollinated flowers. The number of plants which 

 depend upon the transference of pollen by the wind is very 

 great, embracing as it does large families, such as that of the 

 cone-bearing trees (Pine family), the grasses, and the sedges. 



It is easy to see that pollen-carrying by the wind must be 

 a very wasteful process, since only now and then a pollen 

 grain is likely to alight on a stigma of the species of plant 

 which produced it. Accordingly, flowers which have their pol- 

 len carried by the wind yield it in enormous quantities. It is 

 estimated that a medium-sized plant of Indian corn produces 

 about 50,000,000 pollen grains ; a pine tree must produce an 

 unimaginably great number. The stigmas of wind-pollinated 

 flowers which catch the dust-like flying pollen are brush-like, as 

 in the hazels ; feathery, as in most grasses (Fig. 110); or pro- 

 longed and thread-like, as in Indian corn (Fig. 336). Wind- 

 pollinated flowers frequently appear before the leaves of the 

 plant which bears them. What advantage is there in this ? 



113. Self-pollinated flowers. As a rule, inconspicuous flowers 

 with moist, sticky pollen are wholly self -pollinated or can pol- 

 linate their own stigmas when pollen from another flower 

 is not supplied to them. Familiar examples of such flowers 

 are pigweeds, 2 knotgrass, 3 the common chickweed, 4 the round- 

 leaved mallow 5 (Fig. Ill), the low cudweed, 6 and the com- 

 mon groundsel. 7 It is not infrequently the case that flowers^ 

 when they first mature,, have the anthers and the stigma far 

 enough apart to make it impossible for pollen to lodge upon 



1 See Bergen and Davis, Laboratory and Field Manual of Botany, Sect. 149. 

 Ginn and Company, Boston. 



2 Chenopodium, various species. 6 Malva rotundifolia. 



8 Polygonum amculare. 6 Gnaphalium uliginosum. 



* Stellaria media. 7 Senecio vulgaris. 



