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ences because the central topic is a purely botanical one and puts the other sciences under tribute only to the extent that they can help to understand the important phases of the tree's life.
But this typical object, standing in this environ- Types as ment of closely related facts, towers above them, and scientific teaches still higher truths, setting into prominence classes and those larger scientific classifications and laws which interpret the phenomena of nature and of human life on a broad scale. Looked at from the standpoint of botany, the full study of the oak brings out a great type of vegetable growth. The type idea, when clearly revealed by comparisons with other trees and vegetable forms, not only stands as the representative of forest trees, easily observed by all children, but illustrates similar processes throughout all forms of vegetation. Even a child may thus wake up to the presence of great, universal laws, closely observed in a few typical cases, but easily detected in many others. The elaborate study of types is, therefore, the best approach to scientific classes and principles.
Isolate one of these type objects, tear it loose from its root-connections, and it is no longer a type. Its deep setting and intimate vital relation to environment constitute a share of its typical character. As the oak tree, uprooted by the storm, lies dead, no longer a type of living forces, so a lesson topic loosened from its natural setting has no life, no vital force as educative material.
In summarizing the points of value in type studies we may note:
1. The type furnishes us a centre around which to collect the material for induction in the first four steps.
2. The type is extremely concrete while strikingly characteristic in its exhibition of generic qualities.
3. The sifting out of the best types in a study gives us a series of great lesson units, or strategic points, whose mastery gives us the control of a whole study.
4. The deepening of the type study uncovers those radical relations between studies which give a real meaning to the term correlation.
5. The general classes and truths, which the types prefigure, constitute the scientific framework of the study and at the same time furnish the nuclei for lesson unities capable of treatment according to the five steps of instruction.
In this chapter three lesson unities are worked out through the five formal steps, for the purpose of illustrating more definitely the inductive-deductive movement in the treatment of such important topics.
To work out such a lesson unity through all the essential steps may require several recitation periods. The lesson on irrigation will take probably four or five recitation periods of half an hour each.
The Irrigation of Arid Lands
First Step. — How can the dry lands of some of our far Western states be watered from the rivers ?
How are our farms and gardens in Illinois supplied with moisture? Do you know of any of our states where there is little or no rainfall on the plains ? Point out on the map the dry region along the eastern base of the Rocky Mountains. What do you know from your geographies of the climate of this strip of country? What business may be car
ried on here? Grazing and mining. heard of people who crossed the "plains"? Where are the plains ? Recall Fremont's trip to the Rocky Mountains.
Can crops of grain or vegetables be raised on the plains ? What are the difficulties? What rivers flow across this region and in which direction ? Would it be possible to get the water from these rivers upon the dry uplands, so as to use them for purposes of agriculture ? Tell what you may have heard of irrigating ditches.
Second Step. — The strip of country just east of the mountains in Colorado is very dry. There is almost constant sunshine, and very little rain, so that, though the soil is good, it bears only a thin, scattering buffalo grass, and most of the year the country looks almost as barren as a desert. To explain fully the process of irrigating by ditches, “The Big Ditch,” which is drawn from the South Fork of the Platte near Denver, is described as follows:
In order to show the position of this ditch and its relation to the river, the mountains, and the slopes, a map of the region about Denver is necessary, showing the South Fork of the Platte River, the mountains and foot-hills, and the slope on which the ditch is laid out.
The South Fork of the Platte River, after draining South Park, breaks through the foot-hills and descends to the northeast through the great plain