10 BRITISH FLOWERING PLANTS chap. 



flowers are on a separate part of the plant, but are 

 set free and rise to the surface, on which they float 

 in some numbers around the female flowers, one or 

 more of the dehiscing anthers coming in contact with 

 the stigmas. 



While some water plants (Utricularia, Hottonia, and 

 Lobelia, for instance) ripen their seeds in the air, by far 

 the larger number after flowering draw the ovary down 

 under water. In many cases the shell of the fruit 

 develops air cavities, which, when the seeds are ripe, 

 carry them up again to the surface, and thus promote 

 dispersal. No doubt in many cases birds carry them 

 from one river or lake to another. It is easy to 

 understand that the seeds and fruits of water plants 

 do not develop wings or parachutes, which in so many 

 land plants serve this purpose ; nor do we find cases in 

 which they are thrown or jerked. 



It would appear that the chances of the ovule being 

 fertilised and the seed coming to maturity are, on the 

 whole, fewer in water plants than in land plants. On 

 the other hand, the constant supply of water renders the 

 vegetative growth more luxuriant. Hence we find that 

 aquatic plants are generally perennial. In our own 

 flora Subularia aquatica and Najas marina are the 

 only annual species. 



Freshwater plants, for obvious reasons, do not reach 

 high latitudes or great altitudes. In temperate regions, 

 however, the species have, as a rule, very wide ranges, 

 not only in many cases round the world, but Qy^n 

 reappearing in islands far from the mainland, mainly, 

 we can hardly doubt, through the agency of water 

 birds. Najas marina is a very good instance. Widely 

 spread in the north temperate zone, it occurs also in 

 Australia, the Sandwich Islands, Canaries, Venezuela, 

 Brazil, etc.^ 



Another remarkable peculiarity of flowers which I 

 think, as I suggested in a lecture to the British Asso- 

 ciation at Belfast in 1874, has reference to their 



' Rendle, Trans. Linn. Soc. (Bot.) ser. 2, vol. v. 



