On the other hand the Sponges (Spongiadm), which were placed amongst animaie on account of the active motile habits of their ova, seemed to be destined to classification again with plants when motility no longer became the distinguishing mark of the two kingdoms. There are, however, other points of structure which still induce the zoologist to lay claim to the sponges. The comllines (Coraltina) which were formerly classed with the sponges, first as plants, then as animals, are now again placed with the Ccramiacem amongst the sea weeds, and have a decided relation to the vegetable kingdom.
From these facts it is very evident that no mere technical definition will enable the naturalist to separate the animal and vegetable kingdoms, and that it is only by observing the structure and functions of organic beings through the whole course of their existence that we can hope to assign them their right position as plants or animals.
In determining the sphere of Botany by the inquiry into the nature of the plant, it will at once be seen that the study of plants cannot be successfully prosecuted without inquiry into time nature of animals. Again, the chemical elements of which plants and animals are formed, exert a great influence through their peculiar properties on the life of these beings. These must be always taken into consideration In speaking of the structure of n plant or the functions it performs. Hence we see that Botany is but the part of a great series of facts in which the inorganic elements, tho cells of Omits, and the cells of animals, are constantly taking a part, In order to study Botany therefore successfully, the first knowledge that is necessary is that of the properties of the elements which enter into the composition of plants and animals. These are more espe cially four, carbon, hydrogen, oxygen, and nitrogen, which on account of their universal presence in plants and nnimals have been called organic or necessary elements. In addition to these are found twelve or thirteen other elements, which not being univereally present may be called occasional or inorganic elements. Sulphur, phosphorus, calcium, potassium, sodium, iron, magnesium, iodine, bromine, silica, are time most compieuotta of these elements. The organic elements enter into various compounds which are found in plants, as sugar, starch, cellulose, protein, chlorophyle, gums, resins, alkaloids, acids, &c. ; whose properties should be studied In order that their presence may be readily recognised in the dissection of plants. In order to accomplish
this, reagents must be employed, as iodine, potassa, sulphuric acid, iron, rind many others, which on being applied to the parte of plants reveal by their action time nature of the vegetable compounds.
One of the most important aids to the study of the structure of plants, and by which time great recant progress in physiology has been made, is the microscope. The textures of plants as well as animals take their origin in cells so minute that they cannot be seen by the naked eye. It is in and around these cells that the active functions of every part of an animal or plant are going on ; and it is only as the botanist gets to know the nature of the changes which the vegetable elements and their compounds undergo in the cells of plants, that he cast comprehend the general laws of vegetable life. Not only is it necessary to the botanist to study these laws by the aid of the microscope, but the general physiologist mei student of the functions of the human body will find it necessary to begin his inquiries by the study of the nature of vegetable cells. It was by following up the researches made by Schleiden on vegetable cells, that Schwann was enabled to demonstrate the cellular structure of the animal body, and thus to initiate a new era in physiology. It is still in the plant that the simplest condition of the cell is observed. It is also in the plant that the greatest chemical activity of the cell exists. The food of animals, and that which constitutes the substance of the tissues of animals, are all formed in the interior of the cells of plants. It is the cell of the plant which appropriates the carbonic acid of the atmosphere, and throws back again into it oxygen gas ; on the one hand depriving it of an agent destructive to animal life, and on the other supplying the agent by which alone animal life could be carried on. It is also in the vegetable cell that the chemist must seek the solution of some of the most difficult problems of his science. The chemist cannot convert carbonic acid and ammonia into protein, sugar, starch, &c.—processes which are going on in every vegetable cell ; he must therefore regard attentively the changes going on in the cells of plants, if he would manufacture the products of the vegetable kingdom' ndependent of its aid.