10 



Göte Turesson 



2. Previous theories and discussion of literature. 



Warming was probably the first who tried to give a detailed account of the 

 peculiar prostrate habit in littoral and other plants, and subsequent writings on the 

 ecology of shore .vegetation contain a good deal of this discussion, although some 

 new points of interest are added. Warming brought together a number of obser- 

 vations in 1909 and discussed the problem at some length. He gives the following- 

 list of North European plants showing plagiotropy when growing on the beach or 

 on dunes : Anthyllis vulneraria, Artemisia campestris, Asparagus officinalis, Astragalus 

 arenarius, Atriplex, Galcile arenaria, Convolvulus aroensis, G. soldanella, Galium verum, 

 Herniaria glabra, Hieracium umhellatum f. dunense, Jasioiie montana var. litoralis, 

 Junipenis communis, Lathyriis maritimus, Linaria odora, Lotus corniculatus, Matri- 

 caria inodora, Medicago lupidina, M. falcata. Ononis repens. Polygonum amphibium, 

 IP. aviculare, P. convolvulus, Potentilla argentea, Rubus caesius, Salicornia lierbacea, 

 Salix repens, Spergida arvensis, Sueda maritima, Taraxacum erythrospermum, Thymus 

 serpyUum, and f. angustifolia, Trifolium arvense f. prostrata, Trifolium repens, Vero- 

 nica serpyUifolia, Vicia cracca, Viola canina, V. tricolor coniophila. 



When this list is compared with those given above it will be seen that quite 

 a number of plagiotropie plants can be added. Several writers, including Abbomeit (1), 

 Eriksson (5), Masclef (16), Massart (17), Witte (34), and Wittrook (35) have 

 contributed to Warming's hst. Warming has found the following rosette-plants 

 strongly plagiotropie: Leontodon autumnalis {see plate), Hypochaeris radicata, Taraxa- 

 cum, Sonchus arvensis, Pinguicula vulgaris, Erodium cicularium, Thalictrum minus, 

 Plantago media, P. coronopus. To this list are added the following plagiotropie spe- 

 cies found by other woi'kers: Androsace lactifiora, A. septentrionalis, Arabis hirsuta, 

 Draha incana, D. verna, Geum urbanum, Hieracium pilosella, Hypochaeris maculata, 

 Pimpinella saxifraga, Plantago major, Banunctdus bulbosus, Saxifraga tridactylites, 

 Scabiosa columbaria, Senecio Jacobœa. 



That plagiotropie plants are found in other parts of the world under similar 

 conditions is certain. Schimper's (22) account of the East Indian strand vegetation 

 is a case in point. Kearny (9) finds the prostrate habit of littoral plants a notable 

 characteristic of the vegetation of Ocracoke Island, North Carolina. It is further of 

 interest to find that prostrate plants are common in desert regions. Both Volkens 

 (27) and Poulsen (20), to mention only two writers among many, describe such 

 forms, and Warming compares these forms with some European plants, such as 

 Artemisia campestris and Herniaria glabra, which also grow on sandy soil strongly 

 heated by the sun. 



The speculation upon the cause of the prostrate growth begins with the rather 

 naive and teleologic view held by some plant-geographers, that the plants wish to 

 »bend before the wind» (Knüth 11). With this theory of adaptive response, imply- 

 ing the inherent power in plants to change advantageously, we are not content. 



