995 



and buried in Ibe soi\ (Cerastinm Edmondstonii, Arabis petraea, Thy- 

 mus serpijlliim, Saæifraga oppositifolia, and we may also include as 

 a slightly different type, Salix herhacea). This spreading form of 

 growth is particularly adapted for loose gravelly soils, and it re- 

 minds one of the decumbent forms assumed by piants like Lotus 

 corniculatus and Viola tricolor when living on the loose substratum 

 of a sand-dune (cfr. Warming, 1897 b, Fig. 7, p. 82, and V. 

 Wittrock, Acta Hort. Bergiani, Vol. 2, Nr. 1, Fig. 4, p. 45). 



None of the species of the rocky flat are provided with long 

 stolons or runners, but those with a spreading branching habit form 

 a transition between the spot-bound type and that which has the 

 power of wandering. Among the decumbent species just mentioned, 

 we can trace a gradual series from the one tj^pe to the other, cor- 

 responding to the development of accessory roots: Arabis petraea 

 comes nearest to the spot-bound type, and Saliæ herbacea is the greatest 

 wanderer. In case of Agrostis canina, which frequently has runners, 

 the form met with on the rocky flåts is distinctly tufted and has 

 only a few very short runners. Several of these species with a 

 branching growth may propagate by the branches becoming rooted, 

 then, losing their connection with the parent, they form independent 

 piants; this is the case with Salix herbacea, Cerastium and Thymus 

 serpyllum. Taking them all in all, the piants of the rocky flat will 

 be found to be almost lacking modes of vegetative propagation, ex- 

 cept that of pseudovivipary. 



The propagation of the species must therefore be effected al- 

 most entirely by means of seed and bulbils. As a rule flowers 

 are abundant, and the ripening of fruit is successfully carried out. 

 The flowers of the dicotyledons are nearly all insect-flowers, open 

 and easy of access; self-pollination may also occur in most of them. 

 All the monocotyledons are wind-pollinated, as is also Salix her- 

 bacea. A remarkably large proportion of the species propagate by 

 means of bulbils, viz.: Sedum villosum, Polygonum viviparum, Fes- 

 tuca ovina, Aira alpina, Poa alpina, and occasionally Aira flexuosa 

 and Agrostis canina. 



Koenigia islandica, an annual plant, is quite unique; in spring 

 (April— May) large nunibers of its small reddish seedlings can be 

 seen on a perfectly bare surface, which only a short time before 

 was under water; the plant succeds in flowering and fruiting 

 abundantly every year, although the summer is so short; on the 



Botany of the Færoes. 64 



