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The matter is capable of disproof however, and such disproof seems to be afforded by the direct evidence of the present condition of the alpine varieties at large, and by many other similar cases. Among these the observations of Holtermann on some desert-plants of Ceylon are of the highest value.
Hence the conclusion that small leaves, abundant rootstocks and short 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.
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.
Instead of discussing this problem from the theoretical side, I prefer to compare those species which are capable of assuming a dwarf stature under less uncommon conditions than those of alpine and desert-plants. Many weeds of our gardens and many wild species have this capacity. They become very tall, with large leaves, richly branched stems and numerous flowers in moist and rich soil.
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