6 Weiss, Submerged Vegetation of Lake Windermere. 



that it impeded the traffic and interfered with the opening 

 and closing of the locks. The same difficulties arose in 

 France and Germany some ten years later when it had 

 spread to those countries The history of its invasion 

 into Europe indicates that it has considerable powers of 

 rapid dispersal, and yet this does not take place by means 

 of seeds, for it is a dioecious plant, and so far only the 

 female plant has been known in England, and in the 

 absence of the male plant it is always sterile. In 

 the rest of Europe, too, only female plants have been 

 found, but in Science Gossips in 1880 (vol. xvi., p. 227), 

 Mr. D. Douglas has recorded the occurrence of male 

 plants in Scotland. Possibly small pieces of the weed 

 are carried by waterfowl or other birds from place to 

 place, for even the smallest detached pieces will root 

 under suitable conditions. Apart from the power it has 

 of rapidly spreading over a large area, its wonderfully 

 vigorous growth in a new country has been of great 

 interest, and the remarkable subsequent decrease of the 

 number of plants when once it had become thoroughly 

 acclimatised. Whether this latter reduction of vegetative 

 vigour is connected with the absence of seed formation 

 is a moot point, but at all events it is an observable 

 fact. Its method of reproduction in Europe is mainly 

 by short autumn shoots, about one to two inches 

 in length, which are formed in the autumn near the 

 ends of the long and straggling summer shoots. They 

 are easily recognisable in the autumn by their vivid green 

 colour, and in spring when the old shoots die away these 

 young branches take root and produce new individuals. 

 Besides these short dense autumn shoots Elodea produces 

 small specialised buds, comparable to the winter buds of 

 many aquatic [)lants, to which the name of " turions " has 

 been given. They have been observed by Alexander 



