388 Transactions. — Botany. 



middle of this century, and in a few years spread over a great 

 portion of the country. It caused an immense amount of 

 harm by impeding the navigation of canals, interfering with 

 the working of water-mills, and by choking the outlets of 

 drainage-works and reservoirs, but of late years has shown 

 signs of decrease. But Elodea is exceptionally well adapted 

 for spreading into distant localities. Its slender branched 

 stems are easily broken into fragments, any one of which is 

 capable of reproducing the plant. In a country like Britain, 

 with its network of inland navigation, it is easy to see how the 

 passage of barges along canals might be the means of carrying 

 the plant from place to place, to say nothing of the trans- 

 porting of the fragments by currents or by aquatic birds. But 

 Vallisncria, though capable of rapid increase in any locality 

 where it becomes firmly established, is not so easily carried 

 to a distance. Its stems are much stouter and heavier, and 

 portions large enough to form fresh plants could not be- 

 carried by birds. Consequently it is hardly to be expected 

 that it will spread by natural means from Lake Takapuna, 

 which has no connection with other lakes or rivers. 



The object of this paper was simply to place upon record 

 the facts connected with the naturalisation of Vallisneria in 

 the colony, and, having done this, perhaps I ought to conclude. 

 But it has occurred to me that there are some questions 

 connected with the life-history of the plant which, although 

 well known to botanists, may not be equally familiar to- 

 others, and which are certainly both curious and interesting, 

 and well worth the attention of any one who takes an interest 

 in natural science. I allude to the remarkable manner in 

 which the flowers are fertilised. "With your permission, 

 therefore, I will give you a brief account of the structure 

 of the flowers and the mode of their fertilisation. 



In the first place, for the sake of clearness, it is perhaps 

 necessary to mention a few facts which are probably known 

 to all who read this paper. In all flowering-plants, before 

 perfect seed can be produced, it is requisite that the pollen, or 

 male element, should be transferred to the pistil, or female 

 portion of the flower. In the vast majority of flowering- 

 plants this is effected in two ways, and in two ways only. 

 These are, first, by tlie agency of wind, which simply blows 

 the pollen from flower to flower. Our pine-trees, oaks, wil- 

 lows, most grasses and sedges are familiar examples of wind- 

 fertilised plants. Secondly, by the aid of insects, birds, or 

 other small animals, who, unconsciously to themselves, carry 

 the pollen from flower to flower. Almost all plants having 

 brightly-coloured or highly-perfumed flowers belong to this 

 class. But in addition to these two main divisions some few 

 plants exist — not numbering more than three or four score — 



