so HYDROCHARITACEAE [ch. 



From the lower part of the stem of the Water Soldier, nu- 

 merous green, unbranched roots hang down into the water. 

 These roots may attain great lengths. On August ii, 1910, 

 the present writer measured three roots, each over 40 inches 

 long, growing from the base of one big plant, while on June 

 30, 19 1 3, seven roots belonging to a single plant, were found 

 to attain an average of nearly 33 inches in length. The rate 

 of growth of these roots is singularly rapid; an elongation of 

 over 2 inches in 24 hours was several times recorded in the case 

 of plants growing under somewhat imcongenial conditions in 

 a London garden^. There is no doubt that, at stages when the 

 Water Soldier is floating freely, these long roots balance it in 

 an erect position ; if they are destroyed it is found that the plant 

 can no longer maintain its equilibrium. 



The classic account of the life-history of Stratiotes aloides is 

 that by Nolte^ which was published nearly a century ago. He 

 describes the young plants as rising to the surface in the spring, 

 sinking at fruiting time and rising again, after the seed has been 

 shed, before finally sinking for the winter. The process appears, 

 however, to be much less regular than would be gathered from 

 Nolte's description^ and no later observer seems to have wit- 

 nessed the rising of the Water Soldier twice during the year. 

 The plants certainly show a gradual rise in the spring and 

 summer, while they sink again in the autumn, but the move- 

 ments probably vary with the depth and composition of the 

 water, and they may be influenced by the achievement or failure 

 of fertilisation. The actual mechanism of the rising and sinking 

 process has now been ascertained*. Stratiotes is apt to frequent 

 water rich in lime^ and the sinking in autumn is brought about 

 by the deposition of calcium carbonate upon the surface of 

 the leaves, until a point is reached at which the specific gravity 

 of the plant becomes higher than that of the surrounding 



1 Arber, A. (1914). ^ Nolte, E. F. (1825). 



^ Geldart, A, M. (1906) and Kirchner, O. von, Loew, E. and Schroter, 

 C. (1908, etc.). 



* Montesantos, N. (1913). ^ Davie, R. C. (191 3). 



