48 HYDROCHARITACEAE [CH. 



cells of the short, thick stem are packed with large, compound 

 starch grains. The stolons bearing winter buds are readily 

 distinguishable, since they incline downwards in the water, 

 whereas those bearing the summer buds are horizontal or turn 

 slightly upwards. By the early autumn (e.g. October i), the 

 turions are ripe and a slight touch detaches them at the absciss 

 layer, which traverses the stolon close to the base of the bud. 

 They sink through the water, owing to the starch with which 

 they are laden, and, since the centre of gravity lies in the solid, 

 basal region, the morphological apex always remains uppermost. 

 If a handful of turions be dropped into a tumbler of water, 

 it is very pretty to see them all balanced erect, only the tiny 

 segment of the stolon, between the absciss layer and the base 

 of the turion, resting on the bottom and forming, as it were, an 

 almost microscopic pedestal. They recall the little tumbling 

 toys made for children, which are so weighted that no treat- 

 ment, however rough, can prevent their coming to equilibrium 

 in the vertical position. 



The turions, which are protected externally by a layer of muci- 

 lage, pass the winter in the mud at the bottom of the water. It has 

 been demonstrated experimentally that they can remain dormant 

 for at least two years without losing their power of germination. 

 The dormancy has been shown to be due to lack of light 1 and 

 can be induced if the buds are not buried but are merely dark- 

 ened. The increased sunshine of spring or early summer is the 

 signal for renewed development. The present writer has found 

 that these turions will readily survive the winter at the bottom 

 of an ordinary rain-water tub. It was noticed in one season 

 that, whereas no plantlets were visible in the tub on May 10, by 

 May 1 5 about seven had risen to the top and were unfolding. 

 This occurred after a long period of warm weather. The de- 

 velopment of the little plants coincided remarkably in point of 

 time ; on May 1 6 they were practically all at the same stage 

 (Fig. 30). In each case the three outer scales had turned back 



1 Terras, J. A. (1900). See also p. 280. 



