COLONISATION BY OTHER METHODS. 57 



absorbing roots. The Bladderwort {Utricularici), the 

 Frogbit {Hydrocharis morsiis-ranae), Salvinia, AzoUa, 

 and the Florida Hyacinth are all similarly independent, 

 and are never attached to the ground. They are easily 

 carried about by the current ; and sometimes show 

 an extraordinarily quick rate of multiplication. For 

 example the Florida Hyacinth {Eichhornia crassipes), a 

 native of tropical South America, was introduced 

 into the St. John's river about 1890. In 1897 it 

 had increased to such an extent that large steamers 

 were rendered helpless through the plants becoming 

 entangled in their paddle-wheels ; timber rafts could 

 not be brought down stream ; and net fishing was 

 stopped altogether. Its chief peculiarity lies in the 

 way in which 20 or 30 plants remain attached to 

 one another by the long runners, rather like those 

 of the strawberry. The petioles of the leaves also 

 are greatly swollen, and act as very efficient buoys, 

 preventing the plant from being overturned. 



Pistia stratiotes also floats in water. There is a 

 special enlarged part of the leaf which acts as a 

 buoy. Many other water plants, although they are 

 normally attached and rooted in the mud, seem to 

 be very slightly affected by the loss of their fixed 

 base. Any part that has been broken off and remains 

 floating in or upon the water, seems to obtain all that 

 it requires, and even to increase and multiply without 

 any trouble. 



Nor is this difficult to understand, for the skin of 

 both the leaf and stem of water plants is, as a rule, 

 scarcely at all thickened, so that water can enter 

 over the whole surface, and a root is not generally 

 essential. There is, in fact, a tendency in plants to 

 lose in water the hard outside thickening which is 



