Botanical Review, 6(5): 181-203 (May, 1940)
Environmental Influence and Transplant Experiments
William M. Hiesey

(exerpt)
EFFECTS OF TRANSPLANTING TO DIFFERENT ENVIRONMENTS

Many common species grow over a wide range of natural conditions, and have distinguishable forms associated with different habitats. Such species may extend from the seacoast inland, from habitats. Such species may extend from the seacoast inland, from a region of heavy rainfall to arid country, from a southern latitude a region of heavy rainfall to arid country, from a southern latitude northward, or from a low altitude to a high one. The plants occurring at the extremes of the range are usually the most unlike, while those from intermediate situations may form intergrading series with the extremes. If a race is transplanted from one habitat to that occupied by another related one, will it become like the form native to the new environment? If it remains distinct, does it undergo any morphological change, and if so, what is the nature and significance of this change?

Kerner (50, 51) was one of the first to investigate these problems. Between 1875 and 1880 he established an alpine garden in the Tyrolese Alps at an altitude of 2195 m., and utilized the botanical gardens at Innsbruck, 569 m., and at Vienna, 180 m., as low-land stations. He grew over 300 species of perennial plants from seed at the contrasting altitudes and compared them over a period up to six years. Kerner found that his plants retained their original specific characters after transplanting, but each was modified to some extent by the change in its environment. Thus, lowland plants brought to the alpine station became lower in stature, had smaller leaves, shorter internodes, smaller inflorescences, fewer flowers, and more brilliant floral tints.

While these changes tended to make the lowland plants resemble superficially the dwarf forms native to higher altitudes, transplanting did not affect their fundamental structural characteristics. It did not transform lowland into alpine races, for the alterations were merely quantitative and within definite limits characteristic of the species. Moreover, lowland races, which are slower in seasonal development than alpines, did not often mature at the high altitude. Only 32 out of 300 species were able to develop flowers during the short growing season at the alpine station. In a few cases, species from low elevations developed ripe seed at the high altitude. These Kerner harvested and sowed at the botanical gardens, where they developed into plants indistinguishable from those which had been kept at Vienna or Innsbruck. Kerner also experimented with annuals, and found that species originally from the lowlands were generally unable to survive at the alpine station. Only a few reached the flowering stage, but stems and internodes on these were shorter and inflorescences less extensive than on the same species grown at Vienna or Innsbruck. Some which failed to flower at the alpine station wintered over and developed new shoots the following spring. Thus, Kerner reported that Poa annua L., Senecio nebrodensis L., Viola tricolor L., and Cardamine hirsuta L., Senecio nebrodensis L., Viola tricolor L., and Cardamine hirsuta L., among other annual species, became perennial in his garden in the Tyrolean Alps.

His investigations led Kerner to conclude that there are two kinds of characters in plants, those which are modifiable and those which are constant through heredity. He attributed hereditary characters to the structure of the protoplasm, while the relations between it and the external environment determined the inconstant or temporary modifications. The reader will recognize a similarity between this view and the current concepts of genetics.

A very different interpretation was given by Bonnier (7, 8, 9) to the results of his much-cited experiments. Between 1884 and 1889 Bonnier planted 203 cultures of various species of perennials at different altitudes in the French Alps and Pyrenees. He chose groups occurring over a wide altitudinal range having distinguishable forms at different levels. Usually lowland and alpine forms corresponded to subspecies and varieties of the same species, but in some cases related plants, generally accepted as different species, were involved in an experiment. Whenever possible, individuals were dug at an intermediate elevation and divided into two or more vegetative parts. One of these was moved down the mountain to a lowland station, while the other was taken to a higher altitude. Soils also were moved in an attempt to keep the edaphic factors constant. Bonnier moved a few alpine plants to low altitudes, but transplanted a far greater number of lowland forms to higher elevations.

Gardens at Mirande (in the Department of Gers), at Paris, and at neighboring points served as low-altitude stations both for the transplant series in the Alps and those in the Pyrenees. In the Alps, stations were established on the Mount Blanc chain at l'Aiguille de la Tour at 2300 m., at points just below the glaciers, and in the subalpine zone near Chamonix at 1060 m. Other trans-plants were variously placed in rocks and declivities at intermediate points. In the Pyrenees, plantings were made in the alpine zone at Col de la Paloume (2400 m.) and at a submontane station at Cedeac (740 m.). Some cultures were also distributed at la Houruette d'Arreau (1520 m.), at Col d'Aspin (1500 m.), and other places in the drainage basin of the Arve.

The cultures established between 1884 and 1889 were observed by Bonnier until 1919, his results being summarized in three memoirs (7, 8, 9). The most striking result which he reported was the gradual but complete transformation of lowland forms into alpine types (9). In the course of eight to thirty-five years, de-pending upon the species, Bonnier claimed that the contrasting forms gradually became morphologically and anatomically indistinguishable. Examples of conversion of one species into another include Helianthemum vulgare Gaertn. which became like H. grandiflorum DC., Polygala vulgaris L. like P. alpestris Rchb., Silene nutans L. like S. spathulaefolia Jord., Silene inflata Sm. like S. alpina Thomas, Lotus corniculatus L. like L. alpinus Schleich., Solidago Virgaurea L. like S. alpestris W. & K., to mention only some of the cases. Much more frequent were the reported conversions of lowland forms into alpine types whose differences were merely of a subspecific nature. Bonnier also found that certain lowland annual species became perennial when grown at high elevations.

Bonnier developed the theory that plants are able to accommodate themselves to a range of habitats, the extent of accommodation varying with different species. He contended that changes in the environment call forth adjustments in form which, in time, become fixed; but when a species is transplanted outside of its natural range of occurrence, it grows poorly or fails to survive, for there are limits to the adjustments it can make. The capacity for morphological and physiological change, nevertheless, is wide, and corresponds to the variation which we find within polymorphic species, and sometimes even to that within groups closely related but generally recognized as separate species. Thus, units generally treated by taxonomists as subspecies, varieties, or minor variations would, by Bonnier's theory, be merely morphological expressions of the same thing in different environments, more or less fixed in character, however, by reason of having been acted upon by their environments over long periods of time.