Parasite
2 of the 6 encyclopedias on this shelf carry an entry for Parasite. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
in botany, the parasites on plants are either animals or vegetables. Some of the latter are of high organization, as loranthus and orobanche among exogens, and epiphytal orchids among endogens. Many cryptogams in certain ferns, mosses, lichens, and fungals are parasites. The roots of the more highly organized parasites penetrate the substance of the herb at whose expense they feed. The lower parasites, by means of their cells, penetrate other cells to live in and on them. In mineralogy, a plumose variety of boracite occurring in the interior of crystals of the same, and resulting from their partial alteration. In zoölogy, an animal which lives in, on, or at the expense of the actual substance of another. Van Beneden divided parasites into three classes: (1) Parasites proper, living at the expense of the organic substance of the hosts, as the tapeworm; (2) commensals, who live with, or on, but not at the expense of their hosts, as sea anemones often live on shells of hermit crabs, and come in for a share of their prey; and (3) mutualists, a class not clearly defined, and now generally abandoned. Leuckhart divided parasites into ecto- and endoparasites, according as they lived on or within, their hosts. Of the latter, by far the larger number belong to the type Vermes. Vertebrate parasites are rare, but exist among the Pisces. Myxine (the hagfish or borer) penetrates the abdominal cavity of gadoids, and feeds on their flesh.
Aiton's Encyclopedia (1910)
a plant or animal that lives at the expense of another. Parasitic animals may live on the outside, as lice and ticks; or they may reside in the interior, as the tapeworm of man and beast. Parasitic plants are to be distinguished from air plants that fasten themselves to the bark of a tree and live mainly on the air or, at most, on rotten bark and plants, and from plants that feed on dead and decaying matter, but the one shades off into the other so that it is difficult to draw a fast line. A parasitic plant sends roots or absorbing branches into the sap wood of its host and feeds on the sap found there. Quite a number of flowering plants are parasites. Some are green, as mistletoe and bastard toad flax; others are waxy, as dodder and Indian pipe . Rusts, smuts, and mildews which attack crops are parasitic fungi. Originally, a parasite was a person, one who sat beside another, a hanger-on at the table of some rich patron, with the probability of winning a welcome by flattery and sycophancy. See Tapeworm ; Mistletoe ; Dodder
What Has Changed in the Last Century
Collier's reported in 1921 that Van Beneden's third class, the "mutualists," was "not clearly defined, and now generally abandoned." The opposite happened: mutualism and symbiosis became central to twentieth-century biology, from the bacteria of the human gut to the fungal partners of nearly all land-plant roots, and Lynn Margulis's work from 1967 onward established that our own cells' mitochondria descend from once-independent bacteria. Modern surveys estimate that something like 40 percent of all known species live parasitically, which makes parasitism one of the commonest ways of making a living rather than an oddity. Aiton's 1910 list also needs one correction: Indian pipe draws nothing directly from a tree, but taps fungi connected to tree roots, a route traced experimentally in the mid-twentieth century.
Written for this edition, 2026.