Birds. 5161 



Remarks on Anacharis Alsinastrum as a Food for Swans, and an 

 obstruction to the Free Migration of Salmon. By John J. 

 Briggs, Esq. 



The rapidity of growth which this plant exhibits is very extraordi- 

 nary. The flood which occurred upon the Trent, between Swarkeston 

 Bridge and Weston Cliff, caused by the breaking up of the great 

 frost in February, 1855, cleared the river of this weed, leaving only 

 the roots. These soon sprouted again, and now it is as plentiful as 

 ever. Immense masses disfigure the shallows, and cover the beds of 

 the deeps. I notice that the plant, when propagating in the river, 

 strikes its shoots in a lateral direction, underneath the mud, six inches 

 or a foot from the parent plant, peeps to the surface of the mud, and 

 then spreads rapidly. The manner in which the plant is introduced 

 into new localities is most difficult to explain : some persons imagine 

 that it is spread by wild-fowl which probably feed upon it, the seeds 

 passing undigested through the stomach. But a few years ago it was 

 scarcely noticed in the Trent, and now it exists in the Derwent, as 

 well as in most of the canals and still waters of Derbyshire. 



The plant I believe only attracted notice in 1842, and yet I am as- 

 sured by two gardeners, who have a good knowledge of plants, that 

 they knew it well more than thirty years ago. That they made no 

 mistake in the species I proved beyond question, and yet if the weed 

 has existed in this country for so long a period it seems almost im- 

 possible that it should have escaped the notice of our botanists until 

 1842, and spread with such rapidity since. 



The fondness of swans for this plant was noticed at Dunse Castle, 

 where they cleared the lake of every particle of it, and then died off 

 to the original pair. An additional proof of their partiality to it may 

 be gathered from the following circumstance. Some time during last 

 year the plant found its way into the mill-dam at Calke (Derbyshire), 

 from which a small stream (perhaps two miles long) runs into Mel- 

 bourne Pool : the swans on the pool, having at that time none of this 

 weed in their own water, swam on one occasion a certain distance up 

 the stream (towards Calke Mill), in which some small patches of the 

 weed had gained a settlement : the circumstance of their finding it 

 gradually led them on until they reached the mill-dam, and, finding 

 an abundance of the weed there, they did not endeavour to return to 

 their own pool, but remained for many weeks feeding upon the weed : 

 during their stay the new pest decreased rapidly. 



xiv. 2 H 



