THE BOOK OF NATURE STUDY 



of winter buds is water-milfoil (Myriophyllum), a plant related 

 to the curious marestail (Hippuris), which is a marsh form, the 

 upper part projecting from the surface of the 

 water. Both seem to be related to willow- 

 herbs, but are much modified to fit them for 

 the aquatic life. Water-milfoil creeps along i : 

 the mud by means of a rootstock, and sends 

 up stems, which are usually completely sub- 

 merged. These slender stems bear numerous 

 whorled, pinnately divided leaves, with fila- 

 mentous segments. The minute flowers are 

 borne on spikes projecting at the surface. The 

 plants occur especially in ditches, and should 

 not be confused with Ceratophyllum (cf. p. 90). 

 One must not forget also the water-crowfoot, 

 a common little plant in ditches, streams, and 

 shallow ponds, which has both submerged and 

 floating leaves. The submerged leaves are 

 much cut and divided, while the floating leaves 

 are divided into three or six rounded lobes, re- 

 sembling those of other buttercups. The flowers 

 are white, and the plant is common and hardy. 

 One other aquatic plant may be named, the 

 monocotyledon Vallisneria, which is not native, 

 but is very commonly sold by dealers in aquatic plants and animals, 

 and is frequently used in aquaria. It is a plant of great botanical 

 interest, and is also very valuable as an oxygen-producer. Vallis- 

 neria has a perennial stem which grows embedded in the mud, and 

 sends up into the water a number of slender grass-like leaves. It re- 

 produces asexually by runners which root on the mud of the bottom. 

 The plants are of two kinds, male and female. The female plants 

 produce a single flower at the end of a long spirally coiled stalk. 

 If the level of the water rises the spiral uncoils, so that the flower 

 always floats at the surface, however deep the water. The male 

 flowers are borne in spikes and are placed on short stalks. When 

 ready to open they drop off and rise to the surface, where they float 

 in among the female flowers and open to shed their fertilising dust. 

 After the female flowers are fertilised the spiral of their stalk 



FlG. 44. Water mil- 

 foil {Myriophyllum 

 alternifoliuni). 



