714 



till it reached its final destination, T verily believe it would be suffi- 

 cient to account for the myriads of individuals that now exist in Eng- 

 land. Indeed, from the circumstance of all the plants hitherto found 

 being of one sex, the hypothesis of its propagation from a single seed 

 or fragment is rendered more probable than by supposing a number 

 of seeds or fragments to have been imported. 



But some one will be asking, as the plant could not have found its 

 way by water from Rugby or Watford to Cambridge, How came it in 

 the Cam ? This question, through the kindness of Mr. Babington, I 

 am enabled to answer distinctly. In 1847 a specimen from the Fox- 

 ton Locks was planted in a tub, in the Cambridge Botanical Garden ; 

 and in 1848 the late Mr. Murray, the Curator, placed a piece of it in 

 the conduit stream that passes by the new garden. In the following 

 year, on Mr. Babington asking what had become of the stick which 

 marked the site of the plant, he was informed that it had spread all 

 over the ditch. From this point it doubtless escaped, by the waste 

 pipe, across the Trumpington Road into the " Vicar's Brook," and 

 thence into the river above the mills, whei'e it is now found in the 

 greatest profusion. In the case of the Cam, then, we see it proved to 

 demonstration, that the short space of four years has been sufficient 

 for one small piece of the Anacharis to multiply so as to impede both 

 navigation and drainage. When Professor Gray, of Boston, U.S., was 

 at Cambridge, Mr. Babington mentioned the circumstances to him, at 

 which he expressed surprise, as the Anacharis is not found to spread 

 in this active manner in America. Perhaps our sluggish streams, the 

 decomposing vegetable and animal matters in our Cambridge waters, 

 and especially the excess of lime present (fifteen to seventeen grains 

 in the gallon), furnishing an inexhaustible supply of inorganic food, 

 may account for its more rapid increase here than in America. 



Lastly, with respect to the question, How is it to be got rid of? 

 I think we may answer it at once, by an emphatic " not at all."* Like 

 the imported European horses and oxen in the South-American para- 

 pas, or Capt. Cook's pigs in New Zealand, or the Norway rat in our 

 own farm-yards, or the Oriental black-beetle in London kitchens, or 

 (more remarkable still) like the exotic moUusk, Dreissena polymorpha, 

 which has now spread itself through the canals of this country, we 

 may conclude it has fairly established itself amongst us, never to be 

 eradicated. All we shall be able to do is to try and keep it down ; 

 and in order to effect tnis it should not be left in the rivers after being 

 cut, in the hope of its finding its way to sea, but be raked out at once 



