United States or Uzbekistan ? Vote for the TOP Country of the Week !
CUCURBITACEAE. The tendrils in this family have been ranked by competent judges as modified leaves, stipules, or branches; or as partly a leaf and partly a branch. De Candolle believes that the tendrils differ in their homological nature in two of the tribes. From facts recently adduced, Mr.
These facts appear to show, not only that there are homological internal relations, but that they are so strong and energetic as to re-assert and re-exhibit themselves in creatures which, on the Darwinian theory, are the descendants of others in which they were much less marked.
Fifthly, tendrils, whatever their homological nature may be, and the petioles or tips of the leaves of leaf-climbers, and apparently certain roots, all have the power of movement when touched, and bend quickly towards the touched side. Extremely slight pressure often suffices. If the pressure be not permanent, the part in question straightens itself and is again ready to bend on being touched.
In this respect they differ from all those previously described, with the exception, perhaps, of the Cucurbitaceae. The homological nature, however, of a tendril seems to make no difference in its action. Vitis vinifera. The tendril is thick and of great length; one from a vine growing out of doors and not vigorously, was 16 inches long.
The homological structure, embryological development, and rudimentary organs of a species remain to be considered, whether it be man or any other animal, to which our attention may be directed; but these great classes of facts afford, as it appears to me, ample and conclusive evidence in favour of the principle of gradual evolution.
They are, in fact, sometimes even more plain and distinct in animals of the highest types than in inferior forms, and, moreover, this deep-seated tendency acts even in diseased and abnormal conditions. Mr. Darwin recognizes these homological relations, and does "not doubt that they may be mastered more or less completely by Natural Selection."
It remains now to consider what are the evidences in support of the existence of an internal power, by the action of which these homological manifestations are evolved. It is here contended that there is good evidence of the existence of some such special internal power, and that not only from facts of comparative anatomy, but also from those of teratology and pathology.
Nor does it ever contract spirally, although a contraction of this kind apparently would have been of service to the plant in climbing. Nevertheless it climbs pretty well without this aid. In the hothouse the tendrils served simply for climbing. The position of the tendrils alone suffices to show their homological nature.
To return, however, to the subject of homological relations: it is surely inconceivable that indefinite variation with survival of the fittest can ever have built up these serial, bilateral, and vertical homologies, without the action of some special innate power or tendency so to build up, possessed by the organism itself in each case.
Mohl, who includes under the name of tendrils various organs having a similar external appearance, classes them according to their homological nature, as being modified leaves, flower-peduncles, &c. This would be an excellent scheme; but I observe that botanists are by no means unanimous on the homological nature of certain tendrils.
Word Of The Day