n] THE ARROWHEAD 17 



occurs in the epidermis. The blue tint seems very constant; it is 

 recorded by European writers and is shown in the coloured 

 illustrations to that splendid Japanese flora, "Honzo Zufu 1 ." 



The store of reserve material, laid up in the tuber for the 

 succeeding year's growth, makes the Arrowhead a potential 

 food plant. In Germany the tubers are sometimes employed to 

 feed pigs under the name of "Bruch-Eicheln 2 ." They are used 

 in Japan 3 , while in China the plant is actually grown for the 

 sake of its tubers, which, in cultivation, reach the size of a 

 clenched fist 4 . The tubers of the related Sagittaria variabilis, 

 sometimes called "Swan's Potatoes 5 ," are said to be eaten by 

 the American Indians under the name of" Wapatoo 6 ." 



By winter time, the decay of the stolons sets the tubers free 

 from the parent plant, which does not itself survive until the 

 next season. In the spring, the apical region of the tuber grows 

 out into an elongated axis bearing scale leaves, and carrying 

 the terminal bud up to the surface of the mud, where it pro- 

 duces a new plant. Food is absorbed from the parent tuber for 

 some time; it is possible to find a plant still attached to the tuber 

 from which it arose (Fig. 7, p. 1 8) and already itself producing 

 the stolons (j/ 2 ) which will develop into the tubers of the next 

 generation. At this stage the parent tuber (/) has given up its 

 stores of food material and is in a dry, spongy, exhausted state. 

 The conditions which influence tuber formation will be dis- 

 cussed in Chapter xvn, when the wintering of water plants 

 comes under consideration. 



The Arrowhead is reproduced by seed as well as vegetatively. 

 The tubers suffice for colonisation of a limited area, but the 

 seeds serve to distribute the species over greater distances. The 

 mericarps, which each enclose a single seed, are flattened and 

 air-containing; they are suitable for dispersal either by wind or 

 water. Their specific gravity is still further lowered by the 

 presence of an oil in the secretory ducts of the pericarp. The 



1 Anon. (1828). 2 Walter, F. (i 842). 



3 Anon. (1895). 4 Qsbeck, P. (1771). 



5 Paillieux, A. and Bois, D. (1888). 6 Buchenau, F. (1882). 



A. W. P. 



