DI'COTYLE'DONS (Neo-Lat.. from Gk. at-, di-. double saseino6v, kot1t/a/(3n, eup-shaped. hollow, from Koran, hot,/le, cavity). The larger and more important of the two groups of flowering plants, angiosperms (q.v.). Its members repre sent the eulmination of the plant kingdom. and are the most eonspienous and the most modern of plants. More than 80.000 species have been descrihed, and the actual number is probably over 100,000. The chief characters which dis tinguish them from monocotyledons, the other group of angiosperms. are an embryo with la tent I cotyledons (usually two) : the vaseular bundles of the stem forming a hollow cylinder. which means all annual increase in t he 11 I a Illetvr of woody steins: an open system of venation, which means that the veinlets end freely in the tissues of the leaf or in the margins, often re sulting in various forms of toothing, lotting, and branching: and flowers whose tendency is to dis play their parts in fives or fours or their multi ples.
great groups of dicotyledons are reeog 161A—the Archichlamydc.• and the Smypetal:e. In the former there is tither no perianth (calyx and or its parts are separate (polypet aloft- : in the latter the corolla is sympetalous petal- coalesced). Formerly the Arehichlamy d,a- %%kne divided into tl10 group.—the Apetahe, in which there are no petals. and the Polypetabe, in which petals are present : but this division has been found to be too artificial to stand, as several natural families have both apetalous and polypetalons members.
An•ifictii.Auvoc.r. These are the simpler and more primitive dicotyledons. and contain ahout 49.intu, or one-hail of the known species Of dicotyledon•. distributed among about 160 families. The prominent may be given as follows: (II great tree assemblage. promi nent in which are the oak, hickory. walnut, chestnut. beech. poplar, elm. willow. rte. These plants are prcbably the most primitive of the dicotyledons. a fact indieated by the simplicity of their floral •trUcturen anti by their anenophi lous Mat ing i habit. I See P01.1.1N 'rms.) Prominent in the group also is the Char acteristic intloreseenee knots la as the :un•ut (q.v.) or catkin: and it is among its members alone that eltalazoganly (q.v.) has been discovered. (2) The buttercups and their allies, a great as semblage of terrestrial herbs. including water blitturtair=. poppies. and mustards: certain notable tree forms, as the magnolias. custard apples, sassafras. etc.; and also the strange group of 'earnivorons ISarraeonia. Dro
1)iomea, t-te.). The rose family Rosa (-etc), whirl' is one of the hest-known and most useful groups of the temperate region., ing, such form- as the ,trawberry. raspberry. Idnehlterry. rose. hawthorn. apple. pear. quince. plum. cherry. peach. etc. (I) The legume fain- ily (Leguminosoe), svhicli is far the greatest fam ily of the Archichlainycle:e, tvliielt contains about 10.000 species. and with flowers elaborately cua structtvl for insect pollination. litre belong- the lupine, clover, locust. pea. bean, veteli, redbud, lomey-loenst. indigo. sensitive plants, etc. (.') The mnbellifer family (Umbellifera-f. Avhi•h is the most highly organized of the eldamyclea. and contain- II as the carrot. parsnip. hemlock, pepper-and-salt, caraway, fennel, coriander. celery. parsley, etc.
SrMI.T:TAI. V, This group is evidently derived from the .\rellieldample:e. and contains the nio•t highly organized of plants. Older of the group are 'llonopetala-' and •fialtiopetahr.' The contains about 111.000 species. distributed among . 1111)11g tile 111111111114.11( :Ire the following: (1) The heath family Erica•-(•:••1, which of shrubby plants, and %cl ich contains such forms as buckle berry y. e•ra:the•rrt. liearlterry. Trailing a r lint is. htatbtr. rhododend nit!, Indian pipe, r•te. 12.1 The Convolvultis forms and their allies. in which the flowers art prom• ineptly r, including the morning . glory. pole monitim. plilux. genii .11, dog.bane. ere. The mini family Il.abiata•) and its allies, contain about and eliaraeleriled by the irregular tno-lipped flowers. Ifere helong, the mini, di( tany, hyssop, marjoram. thyme. balm, sage, catnip, horehound. lavender. rosemary, etc, In allied families ore the nightshade, potato, tomato. tobacco, mullein. snapdragon, toad flax. painted-clip, Nerbena, plantain. (-le. (4) 'I he Composit:P, the greatest and ranking family of the angiosperms. is estimated to c-ontain at 12.000 sprig•. The name of the family suggests the most conspicuous features—namely, the organization of the small dowers into a compact head. which resembles a single flower, formerly called a 'conqlotind tlower.' the very numerous forms are arnica, thistle. dandelion. tiek•eed, heggar-ticks, Spanish needles, ironweed, aster. daisy. goldenrod. rosin NN era, sunflower, chrysant laainuti. ragweed, cockle bur, oxeye daisy, tansy, sagebrush, lettuce. etc.
DICTADI'lcUS. See DirrAxv.