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- 
buds, surrounded by closely-packed leaves, are formed. 
These drop off and sink into the mud, where they remain 
Fie. 19.—Hydrocharis Morsus-rane (FRoGBIT), SHOWING BROAD FLOATING 
Leaves. (SticHtty Repucep. ArrEeR KERNER.) . 
a, brood-bud attached to shoot ; b, 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 howfreely most aquatics 
