The bladderwort is dangerous to fish, for the little fry, when quite small, run their heads and gills into the bladders and are suffocated.
There are a great many kinds of Utricularia, and they occur in most of the great floral regions.
One of them has chosen a very extraordinary and curious situation. It lives inside the little cups of water which, as we have already mentioned, are formed by the leaves of some Bromeliads. The insects in the water which ought to nourish the Bromeliad (Tillandsia) are really used by the Utricularia. Other Utricularias live in damp earth, moss, etc.
It is not only by traps and pitfalls that plants catch insects: many have specially modified hairs which are quite efficient insect-catchers.
Hairs are used by plants for many different purposes, and it is rather interesting to see how quite a simple organ like a hair can be altered. The stinging hair of the nettle has already been mentioned; many grasses possess minute, rough, flinty hairs, which probably prevent snails from eating them. That also is probably the reason of the strong, rough, coarse hairs which cover the Borage and the Comfrey.
Then on the Chickweed and the Bird's-eye Speedwell there are lines of rather long, flexible hairs which at first sight appear to be of no use at all. But if you take either of these plants, and, holding it upright, place a large drop of water on the leaves, you will see that these hairs are intended to carry the water down the stem. The water runs along them. It is a very pretty little experiment, especially if done in artificial light, so that these hairs are, like the root hairs, intended to absorb or suck up water as it passes over them. Then the Edelweiss and the Lammie's Lug (Stachys lanata) are entirely covered with white cotton-woolly hairs: these are intended to keep the water in the plant, and do so as effectually as a rough woollen coat will keep out rain and mist. Silky hairs, downy hairs, and others are found wrapping up the tiny baby leaves in the bud: they probably keep them warm, and perplex and ward off objectionable insects.
But, perhaps, the sticky or glutinous hairs are the most wonderful of all. They are found on many plants, such as Salvia glutinosa,[152] Plumbago, and Catchfly. One can see insects stuck on them and vainly struggling to be free, and the hairs undoubtedly prevent green-fly and other such pests from interfering with the honey of the flower. In some of these cases it has been shown that the body of the insect is actually used as food, but that is more obvious with two interesting plants which specially devote themselves to the capture of insect prey. One of these is very often kept in the Boer farmhouses near Tulbagh, in South Africa, simply to attract the flies, which are a perfect pest in those dry valleys. Another Drosophyllum, the Fly-Catcher, grows on sandy and rocky ground in Portugal and Morocco. This is also used by the peasants near Oporto as a convenient fly-paper.
In both of these plants large drops of a sticky, glistening liquid are secreted by the hairs which cover the leaves. Any small insect alighting on the latter is sure to get covered by the liquid, and in trying to get away will become hopelessly involved in it. It is probably soon suffocated, for the gummy matter will choke the small air-holes by which it breathes. Both these plants are said to secrete both an acid and a digestive secretion.
But we have two plants which are even more interesting in this country.
Walking over the rough marshy pastures or moors of Scotland one is sure to notice, generally on wet peaty and barren soil, a little rosette of bright, yellow-green, glistening leaves. If it is the right season there will be a handsome purple flower whose stalk springs from them. This is the Butterwort (Pinguicula), and it is not a bad name, for the leaves remind one of butter. The whole upper surface of the leaves is covered with tiny glands secreting a sticky, glistening matter. It is said that there will be as many as fifty thousand of these glands on a square inch of the upper surface.