The influence of Artemisia Absinthium on neighbouring plants. (An essay of Experimental Plant Sociology No. III)

Eighteen species of plants, most of which were chosen at random, were sown beside a hedge of Artemisia Absinthium; they were severely injured and in one ease ( Levisticum officinale) even killed by the chemical excretions of the latter within a distance of ± 100 cm; seedlings of Artemisia Absinthium, on the contrary, were not harmed by the plants in the hedge. The experiments were made during two successive summers and in different surroundings; the results were consistent and confirmed those of Bode, notwithstanding the fact that climatic conditions were extremely unfavourable for the excretion of absinthiin and that even during fine weather it appeared to be feeble owing to the sea climate of Leiden. Spells of cold and of heavy rains sometimes kept the excretion so low that temporarily the absinth plants seemed to exert no action at all. Seedlings which had survived the proximity of the absinth in their first year developed normally during the next season. It was demonstrated that the proximity of Atriplex hortensis had no influence on the same test plants which were injured by Artemisia Absinthium and that they were only physically oppressed by Artemisia vulgaris, viz. by its spreading, branches. This makes it probable that it is indeed the absinthiin, excreted by Artemisia Absinthium, which causes this species to be harmful to the surrounding plants. Fresh leaves of Artemisia Absinthium, dug in the soil, reduced the percentage of germination and sometimes also hindered the development of the seedlings of a number of species. Foliage of Artemisia vulgaris had sometimes a similar action, but seldom to the same degree. In the case of A. Absinthium two harmful effects are apparently combined: a too great amount of organic manure and the formation of absinthiin. It will be worth while to examine the ecological importance of Artemisia Absinthium in its natural habitat.