PITCHER PLANTS, in botany, the name given to plants in which the leaves bear pitcher-like structures or are pitcher-like in form. The plant generally un derstood by this name is Nepen thes, family Nepenthaceae, a genus containing nearly 6o spe cies, natives of tropical Asia, north Australia and (one only) of Madagascar. North Borneo is especially rich in species. They are shrubby plants climbing over surrounding vegetation by means of tendril-like prolongations of the midrib of the leaf beyond the leaf-tip.
The pitcher is a development at the end of the tendril and is generally tubular in form and often shows a pair of wings run ning longitudinally on the outer surface. The mouth of the pitch er has a corrugated rim (peri stome) formed by incurving of the margin, the convex surface of which is firm and shining. It is traversed by more or less promi nent parallel ridges, which are usually prolonged as teeth be yond the infolded margin. Above the mouth is the lid (operculum), which varies in size from a small narrow process to a large heart shaped expansion. A study of the development of the pitcher, es pecially in the young pitchers of seedling plants, shows that the inflated portion is a development of the midrib of the leaf, while the wings, which are especially well represented in the terrestrial type of pitcher, represent the upper portion of the leaf-blade which has become separated from the lower portion by the tendril ; the lid is regarded as representing two leaflets which have become fused. The short straight or curved process from the back of the pitcher behind the lid repre sents the organic apex of the leaf.
The size of the pitcher varies widely in the different species, from a thimble to the size of a quart pot. The colour also varies considerably, even in different pitchers of the same individual, according to age, light exposure or soil conditions. Insects are attracted to the mouth of the pitcher by a series of glands, yield ing a sweet secretion, which occurs on the stem and also on the leaf from the base of the leaf-stalk to the lid and peristome.
Embedded in the incurved margin of the rim which affords a very insecure foothold to insects are a number of large glands secret ing a sweet juice. The cavity of the pitcher is in some species lined throughout with a smooth glistening surface over which glands are uniformly distributed ; these glands secrete a watery fluid which is found in the pitcher even in the young state while it is still hermetically closed by the lid. In other species the
glands are confined to the lower portion of the cavity surface, while the upper part bears a smooth waxy surface on which it is impossible for insects to secure a foothold. This area is termed the "conducting" area, as distinguished from the lower or "deten tive" gland-bearing area. Insects, especially running insects, which have followed the track of honey glands upwards from the stem along the leaf, reach the mouth of the pitcher, and in their efforts to sip from the attractive marginal glands fall over into the liquid. The smooth walls above the liquid afford no foothold, owing to the presence of minute waxy scales, and they are drowned. The fluid, as first secreted, is not acid and contains no digestive enzyme, but the presence of an insect causes the glands to secrete both acid and a proteolytic (protein-dissolving) enzyme. The bodies of the insects are thus digested and the products of digestion absorbed by the glands in the pitcher-wall. Thus Nepenthes secures a supply of nitrogenous food from the animal world in a manner somewhat similar to that adopted by the British sundew, butterwort, and other insectivorous plants. In spite of the presence of a digestive enzyme, the pitchers constantly contain an association of living organism desmids, diatoms, Acarina, larvae of Diptera, etc.
The side-saddle plant, Sarracenia, native of the eastern United States, is also known as a pitcher-plant. There are about seven species, herbs with clusters of radical leaves some or all of which are more or less trumpet- or pitcher-shaped. The leaf has a broadly sheathing base succeeded by a short stalk bearing the pitcher, which represents a much enlarged midrib with a wing like lamina. Above the rim of the pitcher is a broad flattened lid, which is also a laminar development. The surface of the leaf, especially the laminar wing, bears glands which in spring exude large glistening drops of nectar. The lid and mouth of the pitcher are brighter coloured than the rest of the leaf, which varies from yellow-green to deep crimson in different species and in individuals according to exposure to sunlight and other conditions. This forms the attractive area, and the inner surface of the lid also bears a large number of glands, as well as down ward-pointing hairs, each one having a delicately striated sur face.