Manchester Memoirs, Vol. liii. (1909), No. 11, 5 



This form has long internodes and leaves, and does 

 not produce fruits very abundantly, a fact which is pro- 

 bably correlated with the scanty illumination it gets in 

 deep water and particularly when overshadowed by 

 Elodea and Potaniogeto7i as is the case in some of the 

 reaches of Windermere. It is a dioecious species, and 

 fruits in May and June, and the spores are said to com- 

 mence to germinate in August and September. It is 

 recorded in the Ninth Edition of Babington's " Manual of 

 British Botany," which was edited by Henry and James 

 Groves, the great authorities, as an annual plant, and the 

 appearance of the old plants in the late autumn was cer- 

 tainly suggestive of their dying down, though Dr. Migula 

 asserts* that they may live for three or four years when 

 growing in deep water. I have been unable to discover 

 whether this species reproduces by vegetative methods as 

 is so common among the Characeae. As this deep water 

 form fruits somewhat rarely, and as it covers such exten- 

 sive areas, it is most probable that it is endowed with 

 some kind of vegetative propagation. 



Elodea canadensis, Rich., the Canadian Pondweed or 

 Water-Thyme is called Water Pest by the Germans on 

 account of the enormous damage it did both to fish- 

 ponds and waterways after its introduction into Europe. 

 Nothing is known of the means by which it was intro- 

 duced, but it seems to have made its appearance first in 

 1836 near Warringstown, in Ireland. In 1842 it was 

 found both near Dublin and also in Scotland, and in 

 1847 it was discovered near Market Harborough and also 

 near Chichester. After that it spread to most of the 

 canals and waterways where it flourished so vigorously 



* JNIigula, \V. " Die Characeen," in Rabenhorst's " Kryptogamen Flora 

 von Deutschland, Oestreich und der Schwerz," vol, 5, 1897. 



