CHAPTER XXX. PONDS The water of a natural pond is crowded with plant-life. Do not go to one in a London park, which is cleaned out by the County Council at intervals, but to one which is left to itself, and you will find it full of interest. [Illustration: Fig. 141. Water Buttercup, showing the much-divided water-leaves, and the simpler leaves rising into the air.] Some of the plants float freely in the water, as do the duckweeds, and others, such as the water-lilies, are rooted in the mud with their leaves floating on the surface, while yet others are rooted in the mud at the bottom and live almost entirely under water, like some of the potamogetons, or curly pond-weeds. The plants which are more or less attached to the muddy bottom, and have floating as well as submerged leaves, are perhaps among the most interesting, for they show two kinds of leaves. Look at a water buttercup, for example (fig. 141); on the surface of the water, or just above it, are the flowers and leaves, which are rather like the leaves of an ordinary buttercup. Follow the stem a little way down under the water, and you will see that the leaves are no longer simple, but are split up into many hair-like divisions, which sway about easily with the water’s movements. These two kinds of leaves are each suited to their position, as you will see if you think about them. The broad, undivided leaves on the top of the water expose their surface to the sunlight and do as much manufacturing of starch as possible, while the soft much-divided leaves below the surface are in keeping with their position, for they allow the current to pass between their fine divisions instead of pushing them up or tearing them, as it must do if they had broad, flat surfaces, which would be overpowered by the strength of the current. Compare these leaves with those of the water-lily. In the lily you find no divided leaves, but they all rise to the surface and float there, spreading their expanded blades on the water. Notice what very long leaf-stalks they have, sometimes eight or ten feet in length. Think how absurd the plant would look on dry land, with its short stem and its huge leaf-stalks, though they are so well suited for floating in the deep water. In the air the long, soft stalks would flop about on the ground, as they need some support, but this they get in the water, which buoys them up and saves them from expending too much material in the formation of strengthening tissue.