314 THE LOWER DICOTYLEDONS. 



will grow and produce only the divided submerged leaves. 

 Experiments of this kind should be made : sow in damp soil 

 the seeds of submerged forms, sow in water those of mud- 

 inhabiting forms. 



In all cases the flowers are carried above the surface of the 

 water ; they resemble the flowers of ordinary Buttercups in 

 general structure. The flower-buds are developed below the 

 surface, but do not open until they reach the air. 



Some botanists distinguish nearly 20 British species of Water Crow- 

 foot, but they are probably all varieties of one species (R. aquatilis). 

 The commonest form has the lower leaves submerged and finely cut 

 and the upper ones floating with broad lobes. The commonest mud- 

 inhabiting form is often called Ivy-leaved Crowfoot (R. hederaceiis) ; it 

 has no submerged leaves, its stems root at nearly every node, and the 

 flrs. are very small, the petals being scarcely longer than the sepals ; 

 two others are often regarded as distinct species It. tripartitm, with 

 3-lobed leaves and long narrow 3-veined petals, and R. lenormandi, with 

 kidney-shaped leaves and longer 5-veined petals. 



Examine Water Crowfoots, sketching the leaves and flowers. Com- 

 pare the forms of the leaves in plants growing in fast streams, in 

 ditches, in deep water, in shallow water, in mud, etc. Try to account 

 for the differences and to find out how they are connected with the 

 different habitats of the plants. 



The Water Crowfoots serve admirably to illustrate many points in 

 the biology of aquatic plants (see chapter on Ecology). 



324. Marsh Marigold or Kingcup (Caltha palustris). 

 This plant, which grows in low-lying meadows, marshes, banks of 

 streams, ponds, ditches, and other wet places, has a tufted habit. 



The thick perennial rhizome bears annual shoots, about a 

 foot long, which either grow erect or creep and root at 

 intervals. Most of the leaves arise from the base of the 

 stem and are long- stalked ; the sheathing leaf -base has large 

 membranous stipules which enclose the young buds. The 

 upper leaves, carried on the flowering branches, are smaller 

 than the lower ("radical") leaves and have very short stalks. 

 Cut across stems and leaf-stalks, noting their hollow struc- 

 ture. Blow through a leaf, with (1) the stalk, (2) the blade, 

 dipping into water ; plunge a leaf into hot water. 



Note the large flowers (often 2 inches in diameter), with 

 golden-yellow flower-leaves (sepals), 1 numerous stamens, and 



1 How do these apparent petals differ from the petals of Celandine 

 and Buttercup ? Honey is produced at the bases of the carpels ; the 

 flowers are visited by beetles, flies, bees, etc. 



