~In the ditches~, which often run alongside of hedges, ~we find quite a different set of plants~. The ditches are generally cut out to a lower level than the surrounding bank, and so they often contain water while the rest is dry. In such watery ditches the plants which you will find depend a good deal on the quantity of water in the ditch, and whether it is always there or not. If it is really a wet ditch, you may get many of the inhabitants of the lakes, or if it is a dry ditch where but little moisture collects, you will get only rushes and rank grass. An interesting kind of ditch to watch is one which is well supplied with water nearly all the year round, but may dry up during the height of summer. In such a position as this you are nearly sure to find many pond-dwellers, such as water-cress, duckweed, water parsnip, water buttercups, bulrushes, reeds, and many others, which will vary with the locality. These plants generally choose a spot where there is a permanent supply of water, but plants cannot foresee the unexpected draining of the ditch, or a summer drought, and they are sometimes left through these causes to grow on bare mud. When this happens, notice how they behave; those which were already rooted in the mud may continue to flourish for some time, while those which were floating may be able to root themselves and tide over a short danger. If the water is permanently drained off, however, they gradually have to give in; they seem to draw themselves together and the long, luxuriant branches die off, only the short shoots remaining, which are not so extravagant with water. The duckweeds, which you know very well as little floating green leaves, have long, thread-like roots hanging from them unattached to the soil. When the water goes, they first root themselves in the soil with these water-roots, but if the drought lasts long the roots die away and the plant hides in the mud, where it can remain for a long time waiting for the return of the water. [Illustration: Fig. 139. Duckweed, with simple leaves and long roots hanging in the water.] In the ditches you will probably find a number of green, thread-like algæ; these may also remain on the mud for some time when they are dried up, and in their case some of the cells at such times get a specially thick coat, and remain living for long. Then, if the water returns, it is again the home of these algæ, which rapidly grow out from their protected cells.