"Broadly stated, the grand influence which the distribution of moisture over the earth's surface exercises upon the distribution of plants is that the earth is girdled round, in and near the borders of the two rainless zones, which run like a belt round the earth near the two tropics, and separate the region of the periodic rains from the region of irregular rains by two broad belts of country, in which the xerophilous plants predominate more decidedly than they do in any other part of the world, and that they run out from these belts into the interior of the continents, both towards the equator and the poles, avoiding the insular climates.

"The concomitants in plant-form of the xerophilous type of constitution are as follows : In dicotyledons (or netted-leaved plants) - 1st, leaves becoming thick and fleshy, with pulpy inner and leathery outer layers, in which the air passages and stomata are few, and the cells either small or their walls thickened by secondary deposits of cellulose, as shown in mesembryanthemum, sedum, cotyledon and sempervivum ; 2nd, the stem condensed into a single central, unbranched, barrel-shaped or top-shaped mass, which is either leafless, and armed only with spines, as in mamillaria, echinocac-tus and various euphorbias, or without spines, and bearing fleshy or rigid leaves, as in cycads, welwitschia and Vitis Bainesii and V. macropus; 3rd, branching, fleshy, or hard stem types, without proper leaves, but in which the main stems or petioles put on a leafy appearance, as i n opuntia, phyllocactus and the phyl-lodineous ac-cacias ;* 4th, much branching shrubs, with copious whip-like branches without either leaves or prickles, as rhipsalis, cassytha, and Euphorbia Tiruealli; 5th, much branched wiry herbs or shrubs, with an excessive development of prickles, as gum acacias; 6th, shrubs with small, hard, rigid leaves, as in the proteaceae and epacris; 7th, leaves, and often also branches, gland-dotted, as myrtaceae. rutaceae and psoralea, or yielding gummy exudations, like myrrh and frankincense ; 8th, flowers protected by an excessive development of scariose bracts, as in heli-chrysum and gomphrena ; 9th, dense hairiness or scur-finess on the leaf, bract, and other foliar organs ; 10th, in the development of a tuberous root, large out of all ordinary proportion in comparison with the stems and leaves that come from it.

"In monocotyledons (or parallel-veined plants) we have the xerophilous type represented in two very characteristic forms; the large, thick, fleshy-leaved type, as illustrated by aloe, gasteria, haworthia, four-croya, agave and bulbine ; and the familiar bulb type, to which so many of our most beautiful open air garden flowers belong - lilies, tulips, hyacinths, daffodils, cro-cusses, colchicums, ixias - plants which mostly inhabit, not the heart of the rainless tract, but its borders, where rain comes but seldom and sparingly, and which push up into the leaf and the flower in the brief season of fertility, and spend the rest of the year in the form of an underground mass of dry or fleshy leaf-scales, in axils of some of which new plants are formed by a process of vegetative reproduction which enables them to hold their ground even if no seed be ripened.

"One of the most remarkable points about these xerophilous plants is the extraordinary way in which many familiar groups of plants, which are distributed through different climates, are modified in form in the xerophilous belts. We have an excellent instance of this in euphorbia, which is a genus of 700 species, spread over all parts of the world, all the members of which coincide in the extremely peculiar structure of the flower. About 600 of the species are annual or perennial herbs, several of them widely-spread garden and cornfield weeds, with slender unarmed stems, and a copious development of scattered, entirely sessile, simple leaves. About a hundred species inhabit the specially xerophilous region, and these, whilst retaining absolutely their floral structure, become so extremely modified in habit that they are usually taken for cactuses by inexperienced visitors to our living collections.

"The large floras of decidedly xerophilous type are five in number; two in the northern and three in the southern hemisphere, and are as follows:

" 1st. The desert flora, extending from the Canaries, through the Sahara, and through Egypt and Arabia to the Indus delta. This is not so rich in large groups and large genera of decidedly xerophilous type as some of the others, but it is the largest arid tract in the world, and has a great many endemic genera and species.

"2nd. The flora of southern California, New Mexico, Texas and north Mexico, running out northward to Utah and Kansas, but stopped in a southern direction by the Mexican Andes. This is the exclusive home of agave and its allies, fourcroya and beschorneria, and of the rigid-leaved tree liliaceae, yucca, hesperaloe, dasy-lirion and beaucarnea, and it is the great center of the cactuses.

"Turning now to the southern hemisphere, we have:

" 3rd. The flora of southern Angola, stretching down the coast to the mouth of the Orange river, and across the Kalihari desert and Cape Karroo to Kaffirland. This is the great home of aloe (of which one large arborescent species is said to reach 150 feet in the spread of its branches), gasteria, haworthia, stapelia, mesem-bryanthemum (of which latter genus alone there are said to be not less than 400 species of extremely varied habit), and of the cactus-like euphorbias. This is the richest xerophilous flora in the world.

•Many of the acacias do not possess true leaves, but the petioles or leaf-stalks are flattened and leaf-like. These petiole-leaves are called phyllodia. Most of our greenhouse acacias are phyllodineous. - Ed.

"4th. The flora of Central Australia, including the Swan river territory, and reaching on the north to the tropic, and on the south to the Victorian Alps. Here there are no cactuses, stapelias, agaves nor aloes, and crassulaceae is only represented by bryophyllum. The fleshy-leaved dicotyledons are represented by zygo-phyllum, calandrinia, two or three species of mesem-bryantbemum, and several chenopodiaceae; and the fleshy endogens by bulbine. There are not less than 270 species of acacia.

" 5th. The flora of the Chilian province of Atacama, which extends on the west side of the Andes from the borders of Bolivia to 28° to 300 south latitude, and in the heart of the continent of Catamarca, Tucuman, Cordova, Mendoza, and other provinces of the Argentine Confederation. Here there are no agaves, aloes or stapelias, and. scarcely any crassulaceae, but a great many cactuses and the cactus-like euphorbia are represented by one, and mesembryanthemums by two or three species".