Progress in the United States.— At the beginning of the 19th century the advancement of botany in North America was largely in the hands of physicians, through their requirement of a knowledge of plants as materia medics. Professors of botany were unknown. Linnaeus and other great botanists in Europe had had American correspondents, and geographic expe ditions accompanied by European botanical col lectors had touched the margins of the conti nent. Some botanical explorations, chiefly by European visitors, had been effected east of the Alleghany Mountains. The centre of botanical activity was at Philadelphia, among the mem bers of the American Philosophical Society. With Lewis and Clark's expedition across the continent to the mouth of the Columbia, in 1803-06, began a series of American explora tions of the great interior, directed first to the Louisiana Purchase, then to Oregon and finally to California. These were supplemented on the north by the British expeditions of Sir John Franklin and others in quest of a North west Passage. In the fifties began the Pacific Railroad surveys and these were followed by the geological surveys. All these contributed ma terials for the discovery, description and order ly arrangement of the North American flora, the collections going largely into the hands of Thomas Nuttall at Harvard University, John Torrey at Columbia, Asa Gray, who was Nut tall's successor, and George Engelmann, a phy sician of Saint Louis. Meanwhile appeared a new factor which was destined to play an im portant part in the development of botanical science in America, the establishment of agri cultural colleges in the late sixties. These institutions created a demand for a class of botanists who did not exist in the United States or anywhere else, botanists who had brought a critical scientific training to bear on the hard problems of agriculture. For the succeeding two decades the universities of the country, including some of the agricultural colleges themselves, were busily engaged in educating the required men, a movement which resulted in the preparation of many who were competent not only to act as teachers of botany in the agricultural colleges but, a still more important matter, to act as investigators in agricultural experiment stations, one of which was estab lished in each of the States and Territories in the late eighties. The branch of botany which received its greatest impulse was pathology, the science of the diseases of plants. Plant pathol ogy has already been carried to a point of high scientific development and practical appli cation attained in no other country. Syste matic, or, as it is now more commonly known, taxonomic, botany has made rapid strides for ward in the past two decades, largely through the application of methods developed and perfected by American botanists. These methods differ from others chiefly in a full con sideration of the geographic relationships of plants and the examination of very large series of specimens. A revision of the whole North American flora along these lines and accom panied by systematic botanical exploration is now under way. For the future two lines of inquiry are likely to be conspicuous in Ameri can botany, first, the principles of heredity in plants and the applied phase of the subject, plant breeding on a scientific basis; and second the correlation of plant functions with plant structures, a work which will have far-reaching importance in broadening our understanding of the processes of nature. Forestry has assumed an unrivaled importance with the exploration of Alaska, the botany of the semi-arid region is being studied, and bacterial botany occupies some of our best minds. The geographic loca tion of American botanical research has under:.
a profound change as a result of the Spanish-American War. The area to which up to that time the energies of American botanists had been chiefly directed was the north temper ate belt of one hemisphere, but they now must deal in addition with botanical problems in the tropics of both the New World and the Old World.
The plant kingdom is divis ible into five great groups, the Myxophyta, or slime molds; the Thallophyta, including the bacteria, alga, fungi and lichens; the Bryophyta, including the liverworts and mosses; the Pteridophyta, including the ferns and their al lies, and the Spermatophyta, or flowering plants. The first four of these are often jointly desig nated as the Cryptogame, or cryptogams, in con tradistinction to the Phanerogamce, an older name for the flowering plants.
The Myxophyta, or slime molds, known also as the Myxomycetes, Mycetosoa and Myxothat lophyta, are organisms which though usually treated as belonging to the vegetable rather than the animal kingdom, have no cellulose walls covering the cells of which they are com posed; pass a part of their life as plasmodia, or masses of naked creeping protoplasm similar to the animals known as amcebm; and are repro duced without even the simplest method of sexual regeneration. Most of them resemble fungi in that they grow upon decayed animal or vegetable matter. The Thallophyta include a wide variety of plants, associated with each other by exclusion, on the one hand, from the animal-like Myxophyta, and, on the other, from the Bryophyta and higher plants. The plant body is commonly not differentiated into stem and leaf and may even be unicellular; a cell wall is usually present; chlorophyll is often wanting and frequently sexual reproduction does not exist. Among the important groups belonging to the Thallophyta are the Schizo mycetes, or bacteria; the Schisophycea, or blue green algae; the Euphycee, or true algae, includ ing the diatoms, desmids, green alga:, stone worts, brown algae and red algae; the Eumy cetes, or true fungi, and the Lichenes, or lichens. The Bryophyta, or liverworts and mosses, are small plants, having in their life cycle a sexual generation in which the sexual organs are borne on a plant body usually differentiated into stem and leaves, followed by a non-sexual genera tion, which consists of a stalked or sometimes sessile spore-bearing capsule remaining attached to• the plant body of the preceding generation.
The female organ of reproduction consists of an oosphere in a sac called an archegonium, the walls of which are made up of many cells, much more complex structurally than the female organ of the Thallophyta. The male or gan consists of motile antherozoids produced from an antheridium. The group consists of the Hepatica, or liverworts, some of which have a flat scale-like body called a thallus, and of the Musci, or mosses. The Pteridophyta, represented by the ferns, resemble the Bryo phyla in their sexual organs, but differ in the possession of what is known as vascular, as opposed to merely cellular, tissues, and also in that the asexual generation becomes a large plant and maintains a separate existence inde pendent of the earlier generation. The group includes, besides the true ferns, the grape ferns, jointrushes, clubmosses, quillworts and a few others. The Spermatophyta, or flowering plants, also known as Anthophyta or Phanero game, find their essential difference from the Pteridophyta, not in the production of flowers, but in the relationship of the sexual and the asexual generations and in the character of the sexual organs and their embryonic product. In an ordinary fern the sexual generation is a small flat green organism, resembling a thallose liverwort, growing on the ground or other sub stratum and deriving its nourishment from it, but in the Spermatophyta the sexual generation is reduced to almost microscopic dimensions, and leads to independent existence but is. en closed within the body of the non-sexual gen eration, the male portion consisting of the pol len grain and the tube that grows out of it when the pollen grain germinates, the female portion consisting of a minute cellular struc ture within the embryo sac of the ovule. It is to be noted that no motile bodies are produced, as in the two preceding groups, and that the fertilization of the ovule results in the develop ment of an embryonic plant called a seed, which is produced by none of the lower groups of plants. The Spermatophyte are divided into two groups, of which the lower is the Gymno spernur, including the cycads, the cone-bearing trees and a iew related families. In these the ovules are borne not in ovaries but naked among the floral bracts, and the sexual genera tion of the female is still comparatively com plex before fertilization and bears considerable resemblance to that of some Pteridophyta. In the other group, the Angiosperms, the ovules are borne in ovaries, and only the simplest rem nant of a sexual generation persists. In this group are the Monocotyledons, including the grasses, palms, lilies, orchids and their relatives, and the Dicotyledones, including the great ma jority of flowering plants. The dicotyledonous and the gymnospermous plants were at one time classed as a group Exogena, in contradis tinction to the group Endogena, which con sisted of the monocotyledonous plants. This grouping of the flowering plants into exogens and end ens, however, is no longer main tained, it having been shown from embryologi cal studies that the gymnosperms should stand next above the ferns. The old division of dicotyledonous plants into Apetahr, Gamopetcds and Patypetala is also now discarded, the fam ilies included under Apetaler appearing not to constitute a real group. They have therefore been interpolated among the families of the re maining two groups, most-of them going with the Polypetahr. All three of the old names have been abandoned, the name Archichlamy dee being now used for the apetalous and poly petalous plants jointly, and the name Sympetake for the gamopetalous plants. The known species of plants as based on recent standard and conservative enumerations of the various large groups are approximately as follows: 400 lots. S9.000 /1.000 Pserillophyta 3,500 Spermatophyto 120, 000 190, 900 Plants in Relation to Geology.— Plants play an important part in the configuration of the earth's surface by the prevention or retarda tion of erosion. This is accomplished by the direct binding action of roots on the soil, by obstructing the run-off of water as it filters through a layer of decaying vegetable matter and by hindering the melting of snow under the shade of a forest cover. Wind erosion of sand or dust soils both on beaches and in arid regions is prevented chiefly by vegetation. In the building up of peat deposits, such as the sphag num bogs of the Northern States, or the Dis mal Swamp, Okefinokee Swamp or the Ever glades, plants are the principal factors. De posits of coal and petroleum are of vegetable origin. The disintegration of rocks is hastened by the presence of living mosses and other plants. The fertility of soils is largely depend ent on the admixture of decayed vegetable matter, or humus; and the so-called nitrifying organisms of the soil, which change nitrates, which cannot be taken up as food by plants, to nitrites, which are readily absorbed, belong to a group of microscopic plants known as bac teria. A very important role in soil fertilization is played by a certain group of plants, the Leguminous, including the clovers, beans and peas. One of the essentials of plant food is nitrogen. Ordinary plants have not the power to take free nitrogen from the air, where it ex ists in almost quantities, but absorb their nitrogen from certain nitrogenous sub stances in the soil. This element of soil fertil ity is soon exhausted. Leguminous plants, how ever, produce on their roots small tubercules containing bacteria which have the power to take free nitrogen from the air in the soil and i put it into a form suitable for plant food. By the death and rotting of the plant the nitrogen thus absorbed from the air is incorporated in the soil and is available as food for all sorts of vegetation. In this way the leguminous plants are almost indispensable for the rehabilitation of soils worn out by excessive cropping.