THE LOWER DICOTYLEDONS. 



313 



yellow flowers. The Lesser Spearwort (R. flammula) is the more 

 widely distributed in wet places, marshes, bogs, etc. ; it is rarely over 



1 foot high, its lower leaves are stalked, and its flowers ( June-Aug. ) 

 about 1 cm. in diameter. The Greater Spearwort (7?. lingua) is 



2 to 3 feet high, its leaves are all sessile, and its flowers (July-Sept.) 

 about 4 cms. in diameter ; it is not nearly so common. 



323. Water Crowfoot (Fig. 122). Under this name are 

 comprised various forms of Buttercup or Crowfoot which 

 live in marshes or streams and have white flowers. 



The Water Crowfoots are very variable and the varieties 

 are connected by intermediate forms, so that systematic 

 botanists are not agreed as to the number of species that can 

 be distinguished. 



(1) Those which grow in fast streams have most or all of 

 their leaves submerged and divided into numerous fine threads 

 the form best adapted to resist tearing by the running 

 water, besides increasing the surface for absorption of water 

 with dissolved salts and gases. 



(2) In those forms which grow in slow 

 streams, ditches, or ponds, there are 

 usually floating leaves (on the surface of 

 the water) as well as submerged leaves. 

 The former are rounded or lobed, not 

 much divided, and bear stomates on their 

 upper surface. The submerged leaves 

 are finely cut, with numerous segments 

 spreading in a circle. 



(3) In forms which grow in shallow 

 water, in marshes and muddy places, all 

 or most of the leaves are of the 

 entire, rounded or lobed, "floating" 

 type. 



We thus get every transition from 

 plants with all or most of the leaves sub- 

 merged and dissected, to plants with all 

 the leaves broad and either floating on 

 the water or raised above it. The inter- 

 mediate forms are " amphibious " ; when the stream or pond 

 dries up, they grow quite well in the mud, bearing only 

 aerial leaves and no finely divided ones. On the other hand, 

 if flooded or transplanted into water in an aquarium, they 



Fig. 122. Partof a Water 

 Crowfoot, showing a 

 floating leaf and two 

 submerged leaves. 



