• Choose a category
• All
• Classic-Fiction

By Root 525 0

that they might never be found without the flowers that emerge from the moss in which they are embedded. Bladderwort flowers are white, yellow, blue, or purple. Some of the epiphytes have such large, beautiful blossoms that they are readily mistaken for orchids, which grow in the same places. Among the latter is U. endresii of Costa Rica, one of the more robust epiphytic bladderworts, which becomes fourteen inches (35 cm.) tall and bears lovely purple flowers, marked with yellow, an inch and a half (4 cm.) broad.

With one or two possible exceptions, all bladderworts bear the little utricles for which they are named. In length these closed vessels range from about 1/17 to 1/5 of an inch (1.5 to 5 mm.). Although they vary greatly in structural details, all appear to capture their diminutive prey in the same manner, by sucking them in, much as in a laboratory we pick up a tiny swimming creature in a pipette by permitting its flexible rubber cap to expand at the critical moment. To understand how this works, we must look closely at the structure of a trap, taking as our example the Greater Bladderwort. In warm weather the richly branched leaves of this plant become long, and at the height of summer two hundred of these little suction traps have been counted on a single large leaf, but this is an unusual number; only a dozen or so are more commonly found. About one-eighth

Page 120

Greater bladderwort, Utricularia vulgaris, aerial flowering stem and submerged

leaves with bladders

Page 121

Greater bladderwort, Utricularia vulgaris, bladder viewed from the front

showing valve and appendages around the orifice. From a drawing by

the author.

Page 122

Greater bladderwort, Utricularia vulgaris, bladder with one side removed

to show internal structure. Drawing by the author.

of an inch (3 mm.) long, the bladder has a strongly arched dorsal side and a nearly straight ventral side, to which is attached the short stalk that joins it to a segment of the leaf. The mouth, or doorway, at the other end, is directed obliquely downward. Its upper edge is straight, its lower edge a semicircle. From each corner of the mouth springs one of a pair of long, branched appendages, which Darwin called antennae, from their resemblance to the antennae of a small crustacean. From the sides of the mouth below these appendages diverge a number of hairs, several cells long and one cell thick, which may funnel small swimming or creeping creatures to the entrance. The bladder's light green, translucent walls, only two cells thick except where traversed by a vascular bundle along the top and bottom, impart an aspect of delicacy.

The semicircular valve that closes the orifice is attached by its straight upper margin and partly along the sides but free along its curved lower edge, in the center of which it bulges outward. From this convexity spring four bristles in two pairs, the triggers that release the valve. Its unattached lower edge presses firmly against

Page 123

Greater bladderwort, Utricularia vulgaris, bladder set (right) and same

bladder expanded after touching valve with needle. Camera lucida

drawings by the author.

the thick, multicellular sill in such a manner that it can move inward but not outward. A delicate membrane, called the velum, helps to make the joint watertight. Glands that secrete a mucilage apparently attractive to animalcules thickly cover valve and sill. A small creature entering through the door finds itself in a closed chamber with walls covered with four-armed hairs, Darwin's quadrifids. The outer or anterior pair of arms are directed more or less sideward, while the longer posterior pair point inward. The latter are longest at the entrance and become progressively shorter toward the bladder's stalk. This vessel's outer surface, like the plant's leaves and stem, bears many glands with round, slightly projecting heads.

The traplike construction of the bladder is obvious. A small aquatic creature, impinging upon the valve or its trigger hairs from the outside, readily