While deserts seem to be the most unfavorable places in which plants can exist, and their very existence in many deserts is often a precarious affair, it should be kept in mind that the soil of such places is often by no means sterile. As we found in the section of this book on “How Plants Get Their Food,” water is absolutely necessary for the absorption of food through the root hairs. Where, as in an oasis in the desert, water is locally plentiful a luxuriant vegetation springs up, and one of the most fertile parts of our Southwest was transformed from a desert by irrigation. Then, too, in many deserts there is a pronounced rainy season during which there is a marvelous development of showy flowering herbs that die down as rain ceases or becomes too slight, to wait for another opportunity to make the desert blossom into often gorgeous coloring.
Rain forests, temperate forests, grassland, and deserts—all are immense developments of plant societies depending upon climatic differences for their occurrence. There are some other plant communities which also depend for their development on still other differences of climate. Two such are the vegetation of mountain tops in the tropics, and that strange tundra vegetation near the poles which lives all its life on the ice, only the roots and soil in which it grows thawing out during the brief summer. Temperature rather than rainfall is the cause of these and some other plant societies of more local occurrence.
But what of such well-known plant societies as bogs, in which peat is formed, or the plants growingalong the sea beaches all over the world? These, and scores of other plant communities play their part in the distribution of plants, but nearly all of them depend not upon climate, but upon usually purely local conditions of soil. Sandy, actually nearly sterile soil, the acidity of cranberry bogs, the alkaline regions in our own West, the salt lakes and inland seas, regions below sea level, the serpentine outcrops, all the hundred and one differences which local conditions exhibit—all these have a very direct bearing upon plant distribution. It is impossible here to go into the details of the different sorts of plant societies which inhabit such specialized places, nor into the truly wonderful adaptations of certain species to peculiar conditions. But in looking at the vegetation of regions through which one travels it must never be forgotten that its general type, such as forest, or grassland, or desert, or what not, is the result of usually widely operating climatic forces, while many, often quite extensive, plant societies in the region are the result of the local environment. There is often an active struggle as to the dominance of the type dictated by the climate of the place, and the local conditions of soil that tend to nullify general response to it. On Long Island, New York, for instance, there are areas which climatically should produce dense woods of the summer forest type so general all through the Northeastern States. Actually the water-worn sands and gravels that covered the south side of the island in glacial times, are so poor in plant food, that many square miles of this region are now covered only by low scrub oaks and other plants suited to poor soils.
A final word of caution is necessary to those who see in the foregoing brief account of some of thechief causes of plant distribution an answer to questions that many of us ask about why plants or vegetation are of such and such a kind in a particular locality. It has been convenient—nay, it has been necessary—to consider these various factors one by one, but the distribution of almost no individual, and certainly of no widely spread plant community, is the result of any one of these factors operating singly.
The geological history of the region, the links with the past of the species composing the vegetation, the climate, the cooperation of various outside agencies in seed dispersal, the conflict of different species, and of different vegetation types, these and scores of other factors, operating to-day, or having operated in the past—it is all these that are reflected in the plant covering of the earth. The variety and beauty of that covering are too well understood to need further mention here. The extraordinary efforts that the plant world makes to keep all but a minute fraction of the earth clothed with some sort of vegetation we have seen in the pages just turned. No other phase of the study of plant life is so replete with interest as plant distribution. Rightly understood, it is a study, “the cultural, esthetic and practical value of which may well outweigh any other.”
We have now traced, all too briefly and with the many omissions that such a general account as this makes necessary, the broad outlines of plant life. From the architecture of their outer characteristics, which takes up the first chapter, we have gone step by step into the story of what goes on within the plant, and how it reproduces its kind. These actionsor behavior of plants have resulted in many things of great practical importance as well as being of absorbing interest in themselves. What some of these results have been, we see reflected in the uses of plants to man, in the history of their development, and, most of all, in the way they are distributed over the earth to-day.
If plants are still “just plants” to most readers, this book has been written in vain. Those who have gleaned from its pages some conception of what a fundamental thing plant life is, will doubtless want more information than could be included here.
If any considerable proportion of the readers of this volume feel that they have already outgrown it, and that they have many questions about the plant world for which they will have to go to more specialized works for the answer, then this book has more than fulfilled its mission.
FOOTNOTES:[1]After living probably as long as the Big Trees of California, the most famous dragon tree in the world was destroyed by a great storm. It has been replaced by seedlings.[2]A process recently discovered in England for extracting the fiber of this rush by a chemical bath has greatly increased the fiber possibilities of this common rush. Heretofore it has been used only for coarse weaving of rugs and mattings in Japan. By the new process a fine fiber capable of spinning is extracted that may eventually compete with jute.[3]Copyright, 1912. Doubleday, Page & Company.[4]The term “indifferent” in this connection is used to signify that the plant will adapt itself to average conditions.[5]Plants marked thus belong to the heath family and require special conditions as indicated in text.
FOOTNOTES:
[1]After living probably as long as the Big Trees of California, the most famous dragon tree in the world was destroyed by a great storm. It has been replaced by seedlings.
[1]After living probably as long as the Big Trees of California, the most famous dragon tree in the world was destroyed by a great storm. It has been replaced by seedlings.
[2]A process recently discovered in England for extracting the fiber of this rush by a chemical bath has greatly increased the fiber possibilities of this common rush. Heretofore it has been used only for coarse weaving of rugs and mattings in Japan. By the new process a fine fiber capable of spinning is extracted that may eventually compete with jute.
[2]A process recently discovered in England for extracting the fiber of this rush by a chemical bath has greatly increased the fiber possibilities of this common rush. Heretofore it has been used only for coarse weaving of rugs and mattings in Japan. By the new process a fine fiber capable of spinning is extracted that may eventually compete with jute.
[3]Copyright, 1912. Doubleday, Page & Company.
[3]Copyright, 1912. Doubleday, Page & Company.
[4]The term “indifferent” in this connection is used to signify that the plant will adapt itself to average conditions.
[4]The term “indifferent” in this connection is used to signify that the plant will adapt itself to average conditions.
[5]Plants marked thus belong to the heath family and require special conditions as indicated in text.
[5]Plants marked thus belong to the heath family and require special conditions as indicated in text.