xvn] WATER HYACINTH & RIVER LETTUCE 213 



the conclusion that the " individual," which was introduced 

 into this country, has run its course, through an opulent 

 maturity, to a point approaching senility, which may ultimately 

 lead to complete extinction. Water plants certainly appear to 

 offer a favourable field for the study of the " major individual," 

 since, in this biological group, reproduction by sexual means 

 is often deferred for long periods. 



In warmer climates the rapidity of growth of water plants 

 is even more remarkable than in temperate regions. The way 

 in which Eichhornia speriosa, Kunth 1 , the Water Hyacinth, may 

 sometimes choke a wide river, forms a really startling example 

 of excessive quickness of growth and multiplication. About the 

 year 1890, this plant was accidentally introduced into the 

 St John's River in Florida, which, being a sluggish stream, 

 was particularly well-suited to serve as its home. After seven 

 years, two hundred miles of the river bank had become fringed 

 with a zone of Eichhornia from twenty-five to two hundred feet 

 in width. In the summer of 1896, a strong north wind drove 

 the plants up stream from Lake George, forming a solid mass 

 entirely covering the river for nearly twenty-five miles. The 

 growth was so dense that small boats with screw propellers 

 could not get through the mass. Formerly, when the stream 

 was clear, logs used to be rafted down the river, and it is esti- 

 mated that, at the time when the Water Hyacinth was at its 

 maximum, the lumber industry of the region suffered an 

 approximate annual loss of $55,000 from the difficulty of 

 rafting. 



In Africa, the River Lettuce, Pistia Stratiotes^ plays a similar 

 part to the Water Hyacinth of America in hindering naviga- 

 tion. Miss Mary Kingsley 2 gives a characteristically racy 

 description of its behaviour on the Ogowe' and the neighbouring 

 rivers in the French Congo. " It is," she writes, " very like 

 a nicely grown cabbage lettuce, and it is very charming when 

 you look down a creek full of it, for the beautiful tender green 

 makes a perfect picture against the dark forest that rises from 

 1 Webber, H. J. (1897). 2 Kingsley, M. H. (1897). 



