LIFE HISTORIES OF FAMILIAR PLANTS 



Some aquatic plants, like the water lilies, have 

 developed air cavities in the tissues of their leaves, 

 which cause them to float ; then, as I have 

 mentioned in Chapter IX., the leaves take the 

 opposite course and spread themselves out into 

 a rounded form on the surface of the water 

 where they are fully exposed to the atmosphere 

 (Fig. 115, Plate 83) ; the rounded form being the 

 outcome of lack of competition for space. 



Now, the water buttercup holds a unique 

 position amongst aquatic plants for it has, as it 

 were, taken a hint from both the ordinary types 

 of aquatic plants ; it has developed leaves of fine 

 segments like those of the submerged species, 

 and also floating leaves. It is true that its upper 

 leaves often stand above the water instead of 

 floating directly upon its surface, but we must not 

 overlook the fact that the water buttercup has 

 had to modify its original structure, and that at 

 present it is comparatively 5^oung at the business, 

 so to speak. We have only to compare the shape 

 of the upper leaves with those of the buttercups of 

 the field to see readily how the deeply-divided 

 segments of the family type of leaf are being 

 filled in to produce a rounded form. Then if we 

 observe how, when the leaves reach the surface of 

 the water they buoy up the stems, the path that 

 the water buttercup is pursuing is obvious. 



Two further points we should notice with 

 regard to this species. First, that its petals have 

 become almost white, only a small patch of their 

 original yellow still remaining near their base, 



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