Their Nature, Structure, Veins, Epidermis, Stomates.-Effect of Light.- Digestion or decomposition of Carbonic Acid.-Insensible Perspiration. Formation of Secretions.-Fall of the Leaf.-Formation of Buds by Structure of Flowers.-Names of their Parts.-Tendency of the Parts to alter and change into each other, and into Leaves.-Double Flowers.- Analogy of Flowers to Branches.-Cause of the Production of Flowers. Of Productiveness.-Of Sterility.-Uses of the Parts of a Flower.- Changes it undergoes.--Is fed by Branches upon Organisable Matter fur- nished by Leaves.-Physiological use of the Fruit.-Nature of Secre- tions. The changes they undergo.-Effect of Heat-of Sunlight—of Water.-Seeds.-Source of their Food.-Cause of their Longevity-of Limits of Temperature endurable by Plants.-Effects of a too high Tempe- rature of a too low Temperature.-Frost.-Alternations of Tempera- ture.-Day and Night.-Winter and Summer.-Temperature of Earth THE THEORY AND PRACTICE OF HORTICULTURE. HORTICULTURE is that branch of knowledge which relates to the cultivation, multiplication, and amelioration of the Vegetable Kingdom. It divides into two branches, which, although mutually dependent, are, in fact, essentially distinct: the art and the science. Under the art of horticulture is comprehended whatever concerns the mere manner of executing the operations connected with cultivation, multiplication, and amelioration; the science explains the reasons upon which practice is founded. It is to the consideration of the latter subject that the following pages are dedicated. It must have been remarked by all intelligent observers, that in the majority of works upon horticultural subjects, the numerous directions given in any particular ramification into which the art is susceptible of being divided, are held together by no bond of union, and that there is no explanation of their connection with general principles, by which alone the soundness of this or that rule of practice may be tested; the reader is therefore usually obliged to take the excellence of one mode of cultivation, and the badness of another, upon the good faith of gardening authors, without being put into possession of any laws by which they may be judged of beforehand. Horticulture is by these means rendered a complicated subject such as none but practised gardeners can hope to pursue successfully; and, like all empirical things, it is degraded into a code of peremptory precepts. It will nevertheless be found, if the subject is carefully investigated, that in reality the explanations of horticultural operations are simple, and free from obscurity; provided they are not encumbered with speculations, which, however interesting in theory, are only perplexing in practice in the present state of our knowledge. When, for example, refined chemical disquisitions or minute anatomical details, or references to electrical action, are introduced, a plain subject becomes embarrassed with considerations too learned for the majority of readers of gardening works, and having little obvious application to practical purposes. Instead, therefore, of introducing points of obscure or doubtful application, or such as are merely speculative and which only tend to complicate the theory of horticulture, it seems better strictly to confine attention to the action of the simplest vital forces; for the general nature of these has been undoubtedly ascertained, and is easily understood by every class of readers. It is certain, for instance, that plants breathe, digest, and perspire; but it may be a question whether the exact nature of their respiration, digestion, and perspiration is beyond all further explanation; it is therefore better to limit our consideration to the naked fact, which is all that it imports the gardener to know, without inquiring too curiously into those phenomena. For it must always be remembered that the object of a work like the present is not to elucidate the laws of vegetable life in all their obscure details, but to teach, to those acquainted with the art of gardening, what the great principles are upon which their practice is founded. |