158 TRANSACTIONS OF THE [Sess. LXxv. 
from the soil, heath plants disappear and other species take 
their place, such as were mentioned in describing dry 
pasture in general. 
Two associations at least may be recognised :— 
1. Cynosurus-Agrostis association (the usual one). 
2. Poa pratensis association (rich old pasture). 
1. Cynosurus - Agrostis vulgaris association. — Cyno- 
surus and Agrostis vulgaris are the dominant grasses in 
the great bulk of pasture land in the islands. They usually 
occur together, and in some respects it is a natural coalition, 
because Cynosurus is as early a grass as 1s suitable for the 
late northern springs, while Agrostis is very late and may 
remain green all winter. This is even more marked in 
Agrostis alba, which is also prominent, especially in wetter 
situations. In the better pastures Cynosurus may dominate 
almost to the extinction of Agrostis, and, on the other 
hand, is often absent on poorer ground, especially if there is 
a tendency to the development of raw humus in the soil. 
But the individual dominance of either is so much rarer 
than the combination of both in more or less equal 
quantities, that it is better to regard the common type as a 
Cynosurus-Agrostis association, especially since the union 
gives an association with a longer vegetative period and a 
greater production of material. There may be differences in 
their food demands also; at any rate their relationship is 
not one of entire rivalry. 
R. C. Gaut, in the “ Botanical Survey of a Pasture” 
(Naturalist, 1904), concludes that Cynosurus is character- 
istic of poor soils. This appears contradictory to the fact 
that Cynosurus forms most of the best natural pasture 
in Orkney, but the two conclusions are not irreconcilable. 
In England, Cynosurus may be driven to the poorer soils 
by competition of the lustier grasses, Fescues, Foxtail, 
and Cocksfoot, but in Orkney, owing to climatic causes 
probably, they do not enter into competition. Meadow 
Fescue, in fact, grows very poorly even when sown in 
cultivated land. 
Holcus lanatus is usually an important constituent of 
this association. It tends to grow in patches. It may 
even dominate, but associated with Agrostis rather than 
Cynosurus. 
