226 COLIN CLOUT'S CALENDAR. 



and that is near Woodford, in Galway, where it does not 

 appear to have been introduced by human agency. 



It would even have been possible before the days of 

 Columbus for a philosophical botanist of the modern 

 type (had one then been imaginable) to have predicted 

 the existence of the American continent from the occur- 

 rence of so many strange plants in isolated situations 

 on the western shores of Britain and Scandinavia. He 

 would rightly have argued that these unfamiliar weeds, 

 not belonging to any part of the European flora, and 

 sometimes even differing wholly from any known family 

 of European plants, must have come with the prevailing 

 winds and currents from some unknown land beyond 

 the sea. That the plants in question grew there even 

 then is highly probable, because most of them bear every 

 sign of great antiquity : certainly they are not likely to 

 have been introduced by man, since the larger number 

 are mere inconspicuous water-plants, which could not 

 come over with cultivated seeds or tubers, and which 

 would not, of course, be deliberately planted in gardens. 

 On the other hand, when once introduced by chance, 

 they would be sure to gain a firm footing ; because 

 America, with its enormous stretches of fresh water, 

 in rivers, lakes, and innumerable scattered ponds, is far 

 richer in strong and well-endowed aquatic weeds than 

 relatively hilly and lakeless Europe. This peculiarity is 

 well seen in the career of the Canadian pondweed, 

 which was first introduced into England as a botanical 

 specimen in 1847, and rapidly spread through canals and 

 sluggish waters over the whole of Britain. No Euro- 

 pean weed can stand against it ; and what makes its pro- 

 gress the more remarkable is that it seldom or never 



