Darwiniana; Essays and Reviews Pertaining to Darwinism eBook

This eBook from the Gutenberg Project consists of approximately 379 pages of information about Darwiniana; Essays and Reviews Pertaining to Darwinism.

Darwiniana; Essays and Reviews Pertaining to Darwinism eBook

This eBook from the Gutenberg Project consists of approximately 379 pages of information about Darwiniana; Essays and Reviews Pertaining to Darwinism.

What is now to be thought of the ordinary glandular hairs which render the surface of many and the most various plants extremely viscid?  Their number is legion.  The Chinese primrose of common garden and house culture is no extraordinary instance; but Mr. Francis Darwin, counting those on a small space measured by the micrometer, estimated them at 65,371 to the square inch of foliage, taking in both surfaces of the leaf, or two or three millions on a moderate-sized specimen of this small herb.  Glands of this sort were loosely regarded as organs for excretion, without much consideration of the question whether, in vegetable life, there could be any need to excrete, or any advantage gained by throwing off such products; and, while the popular name of catch-fly, given to several common species of Silene, indicates long familiarity with the fact, probably no one ever imagined that the swarms of small insects which perish upon these sticky surfaces were ever turned to account by the plant.  In many such cases, no doubt they perish as uselessly as when attracted into the flame of a candle.  In the tobacco-plant, for instance, Mr. Darwin could find no evidence that the glandular hairs absorb animal matter.  But Darwinian philosophy expects all gradations between casualty and complete adaptation.  It is most probable that any thin-walled vegetable structure which secretes may also be capable of absorbing under favorable conditions.  The myriads of exquisitely-constructed glands of the Chinese primrose are not likely to be functionless.  Mr. Darwin ascertained by direct experiment that they promptly absorb carbonate of ammonia, both in watery solution and in vapor.  So, since rain-water usually contains a small percentage of ammonia, a use for these glands becomes apparent—­one completely congruous with that of absorbing any animal matter, or products of its decomposition, which may come in their way through the occasional entanglement of insects in their viscid secretion.  In several saxifrages—­not very distant relatives of Drosera—­the viscid glands equally manifested the power of absorption.

To trace a gradation between a simply absorbing hair with a glutinous tip, through which the plant may perchance derive slight contingent advantage, and the tentacles of a sundew, with their exquisite and associated adaptations, does not much lessen the wonder nor explain the phenomena.  After all, as Mr. Darwin modestly concludes, “we see how little has been made out in comparison with what remains unexplained and unknown.”  But all this must be allowed to be an important contribution to the doctrine of the gradual acquirement of uses and functions, and hardly to find conceivable explanation upon any other hypothesis.

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Darwiniana; Essays and Reviews Pertaining to Darwinism from Project Gutenberg. Public domain.