166 BRITISH PLANTS 



at any time. During the summer they bloom freely, but 

 few fruits are formed. In late summer and early autumn, 

 when cold, damp weather is frequent, flower-buds form 

 which never open, and these always produce a full com- 

 plement of seed. 



Cross - Pollination. — The poUen may come from a 

 difEerent flower on the same plant (geitonogamy, Gr. geiton, 

 neighbour) or from another plant. Geitonogamy is not far 

 removed from self-poUination, for the sexual elements are 

 both derived from the same plant, though the relationship 

 is not so close as between the stamens and pistil of the 

 same flower. In true cross-pollination two distinct plants 

 must co-operate, one contributing the pollen, and the 

 other the ovules. 



Agents of Pollination. — In self-poUinated flowers the 

 pollen either falls by its own weight upon the stigma or 

 the two are brought into contact by the bending of the 

 stamens or styles. In cross-pollinated flowers an external 

 agent is required to carry the poUen from one flower to 

 another. 



1. Water. — Water carries the pollen only in the case of 

 a few water-plants where the flowers are completely sub- 

 merged aU the time. Most flowering aquatics send up 

 their flowering shoots above water, and these are poUinated 

 in the same way as land-plants. The floral habits of a 

 plant are more conservative than its vegetative organs, 

 and the persistence of the aerial mode of pollination in 

 aquatics affords strong evidence of their terrestrial origin. 

 The grass-wrack (Zostera) found on muddy shores is an 

 example of water-pollinated flowers. It flowers below 

 water. The pollen is long and thread-like, and of the 

 same density as sea-water. It is borne passively to the 

 stigmas by the movements of the water, just as in w'nd- 

 poUinated plants the poUen is carried passively through 

 the air by the wind. 



2. Wind. — In wind-pollinated flowers the poUen is 

 light and powdery. It is produced in enormous quantity, 

 for the wind bloweth where it listeth, and the chance of 

 the pollen reaching its proper destination — i.e.. the 

 stigmas of a flower of the same species — is very small. 

 Anemophilous flowers (Gr. anemos, wind ; phileo, I love) 

 have no need for attractive and sweet-scented corollas. 

 Not being visited by insects, they secrete no honey. The 



