There is one more animal eater which you must try to see, which grows in the water of slow-running streams and in ponds. It is the bladderwort, on which we find very many tiny bladder-like structures on the finely divided leaves under the water. The bladders are built on something of the same plan as a lobster pot, with bristly hairs pointing into the entrance, across which there is a little flap, which makes it quite easy for the very minute animals living in such abundance in the water, to swim ~into~ the bladder opening, but extremely difficult or almost impossible for them to swim out again (~see~ fig. 114). So there they must finally die, and their nourishing juices are absorbed by little compound hairs, many of which are developed on the inside of the bladder. [Illustration: Fig. 114. A single bladder of the Bladderwort, much enlarged, showing the pointed hairs and the flap at the opening.] In the tropical countries there are many kinds of “pitcher plants” with wonderful soup-kettle-like pitchers which catch insects. You may be able to see these plants in a big greenhouse, and should certainly find them in every botanical garden. Notice how large the pitchers are, and that they are really modified leaves which have become different from the other leaves of the plant because of their special work. They generally contain a considerable quantity of water as well as the flies they have caught, and are really “stock-pots” which keep the plant supplied with nourishing, ready-made food in addition to the food which it builds for itself in the green leaves. [Illustration: Fig. 115. Pitcher leaf of Nepenthes, which acts as a “soup-kettle.”] Though these plants have specialised themselves to catch and use animal food, still there are not very many plants that do so, and the old fairy tales about trees with branches which caught men and devoured them, as a sea-anemone catches and devours its food, are only fairy tales, because no such plants exist. CHAPTER XXII. FLOWER STRUCTURES IN RELATION TO INSECTS The relation between flowers and insects is one of mutual help and advantage, and therefore is quite different from that in the cases where the animals eat the plants or vice versa. When we examined flowers in general, we found that the insects do a very important work in carrying the pollen from flower to flower, and that their structures are arranged to attract insects and to make it easy for them to get covered with the pollen of one flower and leave it on the next. If we look at the details in some of the flowers, we shall see how elaborate their structures may be, and how carefully they are planned to make sure that the bee gets the pollen on its body and carries it with it to the neighbouring flowers. [Illustration: Fig. 116. Circular flower of Rose, with many stamens in the centre.]