Page:Popular Science Monthly Volume 15.djvu/28
THE POPULAR SCIENCE MONTHLY.
certain conditions, the rudimentary pistil could be improved and bet- tered, but also the identity of the two pistils, and the high probability that the abortive organ in the one flower was simply the degraded rep- resentative of the well-developed part of the other.
As a final example of the manner in which we receive clews toward the explanation of the modifications of flowers, the case of the wall- flower is somewhat interesting. This plant and its neighbors possess the parts of the flower in fours. (Fig. 1, A.) There are four sepals and four petals, while six stamens (Fig. 1, B) are developed; the pistil possessing only two parts. Here the law of symmetry would lead us to expect either four stamens or eight the latter number being a mul- tiple of four. The clew to this modification is found in the arrangement of the stamens. We find that four of the wallflower's stamens are long (Fig. B, st '), while two (st a ) are short. The four stamens form a regular inner series or circle, the two short stamens being placed, in a somewhat solitary fashion, outside the others. This condition of mat- ters clearly points to the suppression of two of an originally complete outer row of four stamens, and we receive a clew as to the probability of this view by finding that in some other flowers of the wallflower's group the stamens may be numerous. It is hardly within the scope of the present article to say anything regarding the causes of the condi- tions or of the agencies through which the modifications of plants are wrought out. Suffice it to remark that the "law of use and disuse" of organs explains the majority of such cases, by asserting that organs be- come degraded when they are no longer found to be useful to the econ- omy of their possessors. The degradation of a part is to be looked upon as subservient to the welfare of the animal or plant as a whole, and thus comes to be related to the great law of adaptation in nature which practically ordains that
Whatever is, is right.
The animal world presents us, however, with more obvious and bet- ter-marked examples of rudimentary organs than are exhibited by the modifications of flowers conspicuous as many of these latter instances undoubtedly are. Turning our attention first to lower life, we find among insects some notable and instructive illustrations of abortive organs, and also of the ways and means through which the rudimentary conditions have been attained. In the beetle order, the natural or com- mon condition of the wings which in insects typically number four is that whereby the first pair becomes converted into hardened wing- cases, beneath which the hinder and useful wings are concealed when at rest. Now, in some species of beetles, we may meet with certain individuals with normally developed wings; while in other individuals of the species we find the wings to be represented by the merest rudi- ments, which lie concealed beneath wing-cases, the latter being actually firmly and permanently united together. In such a case the modifies-