54 BRITISH PLANTS 



winter a period of rest. During winter most aquatics 

 experience a break in their vegetative development, and 

 in many cases they pass into specialized resting forms. 

 In a few cases the plant merely sinks to the bottom of 

 the pond, and there it remains till spring comes, when 

 it rises to the surface again, and goes on growing e.g., 

 the water-starwort (Callitriche), the hornwort (Cerato- 

 phyllum). In other plants, special resting or brood- 

 bvds, surrounded by closely-packed leaves, are formed. 

 These drop off and sink into the mud, where they remain 



b~ 



FIG. 19. Hydrocharis Morsus-ranoe (FROGBIT), SHOWING BROAD FLOATING 

 LEAVES. (SLIGHTLY REDUCED. AFTER KERNER.) 



a, brood-bud attached to shoot ; 6, same detached and descending to bottom 



of pond. 



quiescent till the spring e.g., Myriophyllum, bladderwort 

 (Utricularia), frogbit (Hydrocharis, Fig. 19), the water- 

 violet (Hottonia), and the pondweed (Potamogeton crispus, 

 Fig. 18). In the arrowhead (Sagittaria), solid corm-like 

 buds are formed. Water-lilies die down to rhizomes 

 embedded in the mud. 



Seeding among perennial aquatics is casual, and in 

 many forms rare. Annuals must produce seed to carry 

 on the race, and in aquatics annuals are very rare. This 

 is not surprising when we consider how freely most aquatics 



