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In Dicotyledoneae, there are about eight families of plants producing
the most important vegetable fibers. Three of the most important families
were mentioned above: the Linaceae (linen), Malvaceae (cotton) and Moraceae
(hemp). The other families produce such products as jute (Tilliaceae),
ramie, (Urticaceae), Sunn hemp (Leguminosae), Kapok (Bombacaceae) and
floss (Asclepiadaceae). Many other types of vegetable fibers with specialized
uses come from other families of dicots, but their products are not
included here.

One dicot, cotton (Malvaceae, Gossypium spp.), holds the first place
in importance in the vegetable fibers. Biologically, this plant (or
several related plants) is fascinating for a number of unsolved problems,
for its unusual construction, and in various commercial ways. First,
there are two major groups of cultivated cotton species: the Old World
species with 13 chromosome pairs and the New World species with 26 chromo-
some pairs. However, the wild species of the New World also have 13
chromosome pairs. The New World cultivated species, with 26 pairs, therefore,
arose by some doubling process, though no conscious effort was made
by the early natives to accomplish this. The interesting fact is that,
of the doubled pairs in the New World cultivated species, one of the sets
was derived from an Old World species type. Since the doubling of the
chromosomes apparently occurred long before there was any recorded contact
between the Old and the New World, the question arises--how did the set
of Old World chromosomes get across the ocean? No satisfactory answer
has yet been provided.

Another interesting biological problem is in the proper classification
and relationships of the genus Gossypium. Traditionally, the genus
has been considered a member of the family Malvaceae, and indeed the