THE EVOLUTION OF PLANTS
and elaborated the pioneer work done on this problem by Mendel.
In summary it may be said that the plant kingdom presents itself to us as a multitude of organisms of various degrees of complexity, ranging from one-celled algae to multi-celled organisms such as orchids and chrysanthemums. The present vegetation of the earth differs profoundly from that of preceding geological ages; and amid all the present and past diversity of form there is evidence that leads to only one conclusion, namely, that the various forms of plant life are genetically related—that the newer and more complex types have been derived by descent (with modification) from older and simpler types. A mechanism has been worked out along lines suggested particularly by Darwin, de Vries, and Mendel, which offers a partial but rational explanation as to how these evolutionary changes may have been and probably have been accomplished.
In particular the fact to stress in such problems as those here discussed is that they cannot be solved by philosophical speculation; they can be solved only by first-hand study of plants themselves. In our quest of the elusive thing we call truth, whether in science, religion, politics, or any other department of human thought, the most conspicuous historical feature we note is change, revision, and continued research for new and more reliable information and interpretation. What one generation ties to, the next rejects, but not in toto. A residuum remains, which we believe represents the truth. Some progress is made by each generation. The discovery of new facts may necessitate the radical revision or even the abandonment of old ideas, but the only things that should cause us grave concern would be the cessation of the discovery of such facts (for each revision takes us one step nearer to ultimate truth) and the closing of our minds, by
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