These curious little desert-plants disprove the Nagelian views in two important points. First, they show that extreme conditions do not necessarily change the organisms subjected to them, in a desirable direction. During the many centuries that these plants must have existed in the desert in annual generations, no single feature in the anatomical structure has become changed. Hence the conclusion that small leaves, abundant rootstocks and short [451] stems, a dense foliage, a strongly cuticularized epidermis, few and narrow air-cavities in the tissues and all the long range of characteristics of typical desert-plants are not a simple result of the influence of climate and soil. There is no direct influence in this sense. The second point, in which Nageli's idea is broken down by Holtermann's observations, results from the behavior of the plants of the Kaits desert when grown or sown on garden soil. When treated in this way they at once lose the only peculiarity which might be considered as a consequence of the desert-life of their ancestors, their dwarf stature. They behave exactly like the alpine plants in Bonnier's experiments, and with even more striking differences. In the desert they attain a height of a few centimeters, but in the garden they attain half a meter and more in height. Nothing in the way of stability has resulted from the action of the dry soil, not even in such a minor point as the height of the stems. From the facts and discussions we may conclude that double adaptation is not induced by external influences, at least not in any way in which it might be of use to the plant. It may arise by some unknown cause, or may not be incited at all. In the first case the plant becomes capable of living under the alternating [452] circumstances, and if growing near the limits of such regions it will overlap and get into the new area. All other species, which did not acquire the double habit, are of course excluded, with such curious exceptions as those of Kaits. The typical vegetation under such extreme conditions however, finds explanation quite as well by the one as by the other view.