Introduction to Plant Geography and Some Related Sciences

Introduction to Plant Geography and Some Related Sciences

Introduction to Plant Geography and Some Related Sciences

Introduction to Plant Geography and Some Related Sciences

Excerpt

Let us begin with a few basic definitions and follow them with some general explanations.

Biology is the science of life, the study of living things, and it has two main branches -- botany, which deals with plants, and zoology, which deals with animals. But whereas every one of us must surely be clear about the differences between the typical plant (which is static, green, and does not ingest solid food) and the typical animal (which is motile, not green, and ingests elaborated food), there remain many 'border-line cases' that are apt to be claimed by both botanists and zoologists. Indeed, each of the characteristics mentioned for one of these primary groups (kingdoms) of living organisms is exhibited by some members of the other, which prevents the drawing of any hard and fast line between all animals and all plants. And even if we add the stipulation that the greenness of plants shall be due to chlorophyll, and that they shall contain the carbohydrate cellulose, there remain many organisms which possess neither feature but still in other ways seem to be plants, and are usually treated as such.

Consequently it seems best in this case not to attempt precise definition but rather to visualize the typical plant as a living organism that is fixed, possessed of cellulose cell-walls, and dependent for its main food-supply upon simple, gaseous or liquid substances (principally carbon dioxide and water). With the aid of chlorophyll in the light, the organism builds up these substances into sugars and other complex materials. The green plant is thus responsible for the fundamental chain of reactions on which almost all life depends. But this partial description excludes many organisms (such as Yeasts and other small Fungi) which are commonly considered to be plants. These 'exceptions' often form major groups although, as we shall see in the next chapter, they may exhibit none of the stipulated main plant characteristics. The description also leaves behind a basic 'hub' of organisms, chiefly of microscopic types, that seem to belong almost as much to one kingdom as to the other. Among . . .

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