POLLINATION AND FERTILIZATION 



139 



3. Flowers with conspicuous perianth, often with odor, 

 often with nectar, usually with moist or sticky pollen, with 

 knob-like or club-shaped stigmas. 



A good example of 1 is the flower of the peppergrass (JLepid- 

 ium) ; of 2, the flowers of the grasses ; of 3, the showy garden 

 flowers, such as lilies, pinks, and roses. 



131. Modes of pollen-carrying. Each of the 

 three groups just described corresponds to a 

 different mode of transference of pollen from 

 anther to stigma. 



The flowers of 1 either themselves carry 

 pollen from the stamens to the stigma of the 

 same flower (for example, by the curving 

 inward of the stamens as the flower matures) 

 or have it carried from stamens to pistil within 

 the flower by insects which visit the flower, 

 usually in search of pollen. Such flowers are 

 said to be self-pollinated. 



In the flowers of 2 the pollen is carried, 

 preferably from a flower on one plant to a 

 flower on another plant, by aid of the wind 

 or, in the case of a few aquatic plants, by 

 water. Such flowers are said to be wind- 

 pollinated or water- pollinated. 



In the flowers of 3 the pollen is carried, 

 preferably from a flower on one plant to 

 a flower on another plant, usually by in- 

 sects that visit the flowers in order to 

 secure food. 1 Such flowers are said to- be insect-pollinated. 



132. Self-pollination and cross-pollination. There is a very 

 great physiological difference between self-pollination (1) and 

 cross-pollination (2 and 3). In self-pollination the male cell 

 and the egg nucleus with which it unites originate in the same 

 flower ; in cross-pollination they originate in different flowers, 

 preferably from flowers borne on different plants. 



1 Sometimes the pollen is carried by birds, bats, snails, or other animals. 



FIG. 121. Pistil of 

 timothy, with feath- 

 ery stigmas 



sti, stigmas. Mag- 

 nified about 20 times 



