ROBERT SMITH ON PLANT ASSOCIATIONS OF THE TAY BASIN. 213 
Scabiosa succisa, L. 
Achillea millefolium, L. 
Senecio Jacobea, L. 
Carduus lanceolatus, Willd. 
Taraxacum officinale, Web. 
Calluna Erica, D.C. 
Fraxinus excelsior (seedlings). 
Thymus Serpyllum. Fr. 
Prunella vulgaris, L. 
Rumex Acetosella, L. 
Agrostis vulgaris. With. 
Festuca ovina, L. 
Galium verum, L. 
Scabiosa succisa, F. 
Achillea millefolium, F. 
Carduus arvensis, Hoffm. 
Centaurea nigra, L. 
Taraxacum officinale, Web. 
Campanula rotundifolia, L. 
Primula acaulis, F. 
Thymus Serpyllum, Fr. (rare). 
Prunella vulgaris, L. 
Plantago lanceolata, F. 
Rumex Acetosa, F. 
Quercus Robur, L. (seedlings). 
Agrostis vulgaris. With. 
Cynosurus cristatus, F. 
Poa annua, L. 
Festuca ovina, L. 
On Tentsmuir very many such changes are going on. We see 
the loose dunes of wind-blown sand being gradually fixed by bent 
grasses {Ammopliila arundmacea^ Host., and Elymus arenarius, L.j. 
From this basis many associations spring up, that of Sphagnum^ or 
some other marsh moss, in the wet parts, Salix repens^ F., on the 
moist sand. Car ex are 7 iaria^ L., on the drier parts. Over the 
Sphagnuin and moss. Erica Tetralix^ F., forms here and there a 
close colony, and further inland Calluna covers the ground. A 
higher development still is reached in the pine and birch woods, and 
culminates in the ploughed fields and mixed tree plantation around 
Earlshall. 
In the clearings of woods such successions of vegetation rapidly 
succeed each other. In the Emmock Woods, near Dundee, on a 
clearing which has been peopled by broom for a number of years, 
the broom now shows signs of dying out. A thick turf of grass is 
superseding it, with Agrostis vulgaris as dominant and Deschampsia 
flexuosa and Holcus lanatus as sub-dominant species. Seedlings of 
trees, especially rowan and birch, are found here and there, showing 
that the wood is beginning to reconstitute itself. 
The natural alternation of pine and birch in a wood has repeatedly 
been observed. This may he due to the quicker growth of birch 
