Anatomical Reduction in Some Alpine Plants

Abstract

Research in the stelar anatomy of the higher plants has shown that climatic changes have been instrumental in bringing about modifications in structure which may be interpreted as indicative of phylogenetic importance. Jeffrey (7) has demonstrated that prolonged periods of glaciation during past geological ages have accelerated the pace of evolution and, because of the changes thus produced, new types of woody or herbaceous plants have been brought into existence. It therefore occurred to the writer that the peculiar ecological conditions on high mountains, conditions bearing a close affinity with those in arctic regions, might show evidences of progression or differentiation engendered by the bleak unsheltered surroundings which do not obtain in closely allied species indigenous to the low lands. Studies of the few alpine shrubs listed below have demonstrated that such an environment has played an important r6le in promoting progressive innovations in the woody stem, which may be manifest either as new or augmented tissues necessary for the welfare of the plant, or as a reduction or elimination of structures not as important in the intensified struggle for existence. The material described in this paper was collected during the latter part of July, i919, on the Presidential Range in New Hampshire, including the mountains Madison, Adams, and Washington. The species. chosen for investigation represent the well-known gnarled and twisted Krummholz growth characteristic of alpine regions. The specimens were secured from sheltered pockets on the lower slopes of the cones and near the upper limits of shrubs. The exact locations were as follows: on Mount Madison near the Appalachian Mountain Club huts at an elevation of 4,825 feet above sea level, on Mount Adams near Edmund'.s Col at an elevation of 4,930 feet, and on Mount Washington on Biglow's Lawn at an elevation of about 5,500 feet. The topography at these stations presents steep slopes, composed of broken and only slightly decayed Devonian granite. Scattered among the boulders, there are occasional patches of thin acid soil which furnish a precarious footing for the few sedges, heaths, willows, conifers, and the like which are able to exist under the antagonistic, edaphic, and climatic conditions. In general on the sides of the cones it is possible for vegetation other than lichens to maintain a grip on the rocks only in the shelter of some protecting boulder or in some slight depression. Only in such places