42 THE BOOK OF NATURE STUDY 



usually eight in number, are inserted on the four-lobed calyx. 

 The flowers are small, apparently almost seated on the leaves. 

 There are two species, distinguished from each other by the 

 arrangement of the leaves on the stem ; the one with opposite 

 leaves is far more abundant than the alternate-leaved. The 

 Cardamines all like damp situations. The best-known species 

 is the Cuckoo-flower, which flowers in early spring. The Cardamine 

 flexuosa is the one found at the edges of streams ; it may be re- 

 cognised by the wavy stem. The different cresses are puzzling ; 

 but the Nasturtiums, or Water Cresses, and the Cardamines are 

 almost the only two genera of the Cruciferae which have pinnate 

 leaves. The genus Nasturtium is quite distinct from the garden 

 Nasturtium, a genus of the Geraniaceae. Another plant very 

 characteristic of slow running water is the Fleabane (Inula dy- 

 senterica). It is found in ditches on the roadside and in wet 

 pastures. All the florets are yellow, the outer ones very spreading 

 and very bright. The leaves are rough above and downy under- 

 neath. This is one of those plants growing in damp situations with 

 cottony instead of smooth leaves. More observation is necessary 

 before it is possible to give any explanation of this fact. A com- 

 parison of the different species of Inula shows a variety of habitat 

 and a corresponding diversity in regard to this character of hairi- 

 ness. Inula Helenium belongs to rich hilly pastures, and has 

 leaves which are nearly smooth above and downy underneath. 

 Inula Conyza (Ploughman's Spikenard) is a still more downy 

 plant, belonging to dry situations. Inula crithmoides (Golden 

 Samphire) is a seaside plant with smooth succulent leaves, whilst 

 Inula Pulicaria (Small Fleabane) resembles Inula dysenteric* in 

 having leaves with a smooth upper surface and a downy under 

 surface. It would be interesting to compare as many different 

 plants as possible of these two species, with a view to discovering 

 whether the. under surface of the leaf is more or less downy the 

 farther the plant is growing away from water. 



THE VEGETATION OF SWIFTLY FLOWING WATER. RIVERS. 

 The plants growing on the banks of a river lead a semi-aquatic 

 existence : their roots and stems are in the water ; their leaves 

 are partly in and partly out of the water ; they flower out of the 



