LEGUMINOSAE, the second largest family of seed-plants, containing about 430 genera with 7000 species. It belongs to the series Rosales of the Dicotyledons, and contains three well marked suborders, Papilionatae, Mimosoideae and Caesalpinioideae.

The plants are trees, shrubs or herbs of very various habit. The British representatives, all of which belong to the are tendrils; in Robinia the stipules are spiny and persist after leaf-fall. In some acacias (q.v.) the thorns are hollow, and inhabited by ants as in A. sp/iaerocep/iala, a central American plant (fig. 2) and others. In some species of Astragalus, Oriobrychis and others, the leaf-stalk persists after the fall of the leaf and becomes hard and spiny. suborder Papilionatae, include a few shrubs, such as Ulex (gorse, furze), C3/f'l.5'llS (broom) and Gerzisla, but the majority, and this applies to the suborder as a whole, are herbs, such as the clovers, M edicago, Melilolus, &c., sometimes climbing by aid of tendrils which are modified leaf-structures, as in Lallzyrus and the vetches (Vicia). Scarlet runner (Phascolus miilliflorus) has a herbaceous twining stem. Woody climbers (lianes) are represented by species of Baulziriia (Caesalpinioideae), which with their curiously flattened twisted stems are characteristic features of tropical forests, and Enlada sraizdens (Mimosoideae) also common in the tropics; these two suborders, which are confined to the warmer parts of the earth, consist chiefly of trees and shrubs such as Acacia and Mimosa belonging to the Mimosoideae, and the Judas tree of southern Europe (C ercis) and tamarind belonging to the Caesalpinioideae. The so-called acacia of European gardens (Robiiiia Pseudacacia) and laburnum are examples of the tree habit in the Papilionatae. Water plants are rare, but are represented by Aeschyaomeric and Nepluriia,

From Strasburgefs Lehrbuch der Bolanik, by permission of Gustav Fischer. Fm. 2.~Acacia spliaerocepllala. I, Leaf and part of stem; D, hollow II, Single pinnule with food-body thorns in which the ants live; F, food F. (Somewhat enlarged.) bodies at theapices of thelower pinnules; N, nectary on the petiole. (Reduced.) tropical genera. The roots of many species bear nodular swellings (tubercles), the cells of which contain bacterium-like bodies which have the power of fixing the nitrogen of the atmosphere in such a form as to make it available for plant food. Hence the value of these plants as a crop on poor soil or as a member of a series of rotation of crops, since they enrich the soil by the nitrogen liberated by the decay of their roots or of the whole plant if ploughed in as green manure. The leaves are alternate in arrangement and generally compound and stipulate. A common form is illustrated by the trefoil or Clovers which

7

V have three leaflets springing Q from a common point (digitately trifoliate); pinnate

leaves are also frequent as

/ in laburnum and Robinia.

In Mimosoideae the leaves

(7 are generally bi pinnate

< { (figs. 1, 2, 3). Rarely are the leaves simple as in

    Baaliiiiia. Various departures

from the usual leaff

type occur in association

with adaptations to different

/i functions or environments.

In leaf-climbers, such as pea

or vetch, the end of the raehis wi, and one or more pairs of

leaflets are changed into

tendrils. In gorse the leaf

t P is reduced to a slender spinelp like structure, though the

leaves of the seedling have

one to three leaflets. In

many Australian acacias the

leaf surface in the adult plant is much reduced, the petiole

being at the same time flattened and enlarged (fig. 1),

heterophylla) showing flattened leaf- frequently the leaf is reduced like petiole (phyllode), p, and bipin- to a petiole flattened in the vertical plane; by this

means a minimum surface

is exposed to the intense sunlight. In the garden pea the stipules are large and foliaeeous, replacing the leaflets, which ip

)

FIG. I.-Leaf of an Acacia (A.

nate blade.

Leaf-movements occur in many of the genera. Such are the sleep movement in the clovers, runner bean (Phaseolus), Robirlia and acacia, where the leaflets assume a vertical position at nightfall. Spontaneous movements are exemplihed in the telegraph-plant (Desmodium gyraris), native of tropical Asia, where the small lateral leaflets move up and down every few minutes. The sensitive plant (Mimosa pudica) is an example of movement in response to contact, the leaves assuming a sleep-position if touched. The seat of the péovergient is the swollen base of the leaf-stalk, the so-called pulvinus g.

Thee stem of the lianes shows some remarkable deviations from the normal in form and structure. In Papilionatae anomalous secondary thickening arises from the production of new cambium zones outside the original ring (M ucuria, Wislaria) forming concentric rings or transverse or broader strands; where, as in Rliyncosia the successive cam- |

biiims are active

ony at two op- ~;, a, /, ,

Hosite tplpintsi ka 2Q§ 5'€,) li at ri on- i e -="' / ,

stem is produced. F

The eumbing / . 'i b

Bauhirzias (Caes- / / I

alpinioideae) / fe P ' “

have a flattened ~stem

with basin- ',

like undulations; ' § W

in some growth

in thickness is

normal, in others

new cambiurn-

zones are found I '

concentrically,

while in others

new and distinct

growt h -centres,

c a c h wi t h i t s

cambiu in-zone,

arise outside the

FIG. 3.-Branch with two leaves of the Sensitive Plant (Mimosa pudica), showing the petiole in its erect state, a, and in its depressed state, b; also the leaflets closed, c, and the leaflets expanded, ll; p, pulvinus, the seat of the movement of the petiole.

primary zone. The climbing Mimosoideae show no anomalous growth in thickness, but in some cases the stem becomes strongly winged. Gum passages in the pith and medullary rays occur, especially in species of acacia and Astragalus; gum-arabic is an exudation from the branches of Acacia Senegal, gum-tragacanth from Astragalus gummifer and other species. Logwood is the coloured heartwood of Haemaloxylari campechianum; red sandalwood of Pterocarpus sarilalirius.

The flowers are arranged in racemose inflorescence's, such as the simple raceme (Laburrlum, Robiriia), which is condensed to a head in Trifaliumg in Acacia and Mimosa the flowers are densely crowded (fig. 4). The flower is characterized by a hypogynous or slightly perigynous arrangement of parts, the anterior position of the odd sepal, the free petals, and the single median carpel with a terminal style, simple stigma and two