8-1 ENGLISH BOTANT. 



a foreign country, have been carefully weighed by Mr. Marshall, and he does noi 

 hesitate to say that he believes it to be a genuine foreigner, brought here most pro- 

 bably from North America. He thinks that since its first discovery in the lock at 

 Dunsc Castle in 18i'2 it has gi-adually been drifted by streams or canals into most of 

 our Midland rivers. Its extraordinary increase of late jears is an argument in favour 

 of its foreign origin ; for, if it be not a new plant in our own rivers, how is it that it 

 never before exhibited this remarkable property of rapid increase? If it be a native, 

 this new faculty has been recently imparted to it — which seems absurd. But allowing, 

 as we must, that it is an introduced plant, and did not exist at all in our rivers till a 

 few years ago, we are curious to know how it got here. Possibly some ardent 

 botanist, amongst specimens received from other lands, may unwarily have let fall 

 into a piece of water some fragment of this inveterately growing weed ; or we may 

 receive Mr. Marshall's suggestion, that it was brought over in some American timber 

 used in the construction of some of the numerous railways which culminate at or 

 near Rugby. We know that American timber is floated in rafts down the rivers, in 

 which case fragments of the weed would adhere to it, or seeds might find their way 

 into the crevices of the wood, and if but one fragment of the plant or but one seed in 

 some moist cranny retained its vitality till it reached England, it is quite sufiicient to 

 account for the myi-iads of individuals now existing in our rivers and ponds. " Indeed, 

 from the circumstance of all the plants hitherto found being of one sex, the theory 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 an interesting 

 question occurs as to how the troublesome weed came to establish itself in the Cam, 

 the classic stream which ought to be safe from such intruders. Mr. Babington tells 

 us that in ] 847 a specimen fi-om the Foxton Locks was planted in a tub, in the 

 Cambridge Botanical Garden, and in 1848 the late Mr. MuiTaj-, 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 tliis 

 point," says Mr. Marshall, " it doubtless escaped by the waste-pipe across the 

 Trumpington Road, into the ' Vicar's Brook,' and from thence into the river above 

 the mills, where 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 

 bufficient 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, 

 this circumstance was mentioned to him, and he expressed his surprise, as the 

 Anacharis is not found to spread in this very rapid manner in America. Perhaps 

 our sluggish streams, the decomposing animal and vegetable matters in the Cambridge 

 waters, and especially the excess of hme present, may be favourable to its develop- 

 ment and form an inexhaustible supply of inorganic food for its nourishment and 

 support. The great practical question arising from all this seems to be. How is it to 

 be got rid of? We quote ~Mv. Marshall's conclusions on this point. He says, in 

 answer to the question, emphatically, " Nor at all ! Like the imported European 

 horses and oxen in the South American pampas, or Captain 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 mollusc (the Drcissena, 

 polijmorpha') which has now spread itself through the canals of this country, we may 

 conclude it has fairly established itself amongst us, never to he eradicated. All we 

 shall be able to do is to try and keep it down ; and in order to effect this, it 

 should not be left in the rivers after it has been cut, in the hope of its finding its way 



