360 MR. В. $. ADAMSON : AN. ECOLOGICAL STUDY 
The roots of Spire occupy slightly deeper layers on the soil than those of 
Viola, Nepeta, &e., but about the same as those of the Oxlip: with the former 
it forms a “complementary ” society *, both seasonably and edaphically, while 
with the latter the society is edaphically * competitive” *. 
In the greater part of this society the Cip is the only representative of 
the genus Primula, but in other parts P. vulgaris may be present in addition 
to, or to the exclusion of, P. elatior. This point is of interest in connection 
with what Miller Christy says of the distribution of the two forms :—— 
“Notwithstanding the immense abundance of the Primrose all round. the 
Oxlip area, I have never deteeted a single plant growing within that area 
except on or close to the margin” ў. In Gamlingay Wood the two species 
for the most part occupy separate areas, bul. with wide margins, comprising 
both species and numerous hybrids. But in several parts of the wood, of 
considerable extent, a mixture of the two species occurs ў. Some of these 
are surrounded by areas of almost pure Oxlip, without a Primrose region 
being immediately at hand. On the other hand, the whole of Gamlingay 
Wood is on the extreme edge of the Oxlip area as defined by Christy t, where 
а complication of distribution might be expected. 
In other Ash-Oak woods in the: district a similar mixing of the two species 
occurs in Byersden Wood; but in Hayley Wood and also in Kingston 
Wood Primula elatior occurs alone. Оп the other hand, in Borley Wood, 
on Boulder Clay above Chalk in South Cambridgeshire, Primula elatior is 
quit ` absent. 
Spirea Ulmaria Society. (b) OPEN TYPE $. 
Another Spiræa Society occurs in other parts of the wood, where the light 
is rather less reduced than in the type described. In this Viola, Anemone, 
and Ranunculus Ficaria are much less abundant. The * prevernal aspect ” | 
is controlled by Primula elatior, often extremely abundant, Ajuga reptans, 
and Nepeta hederacea. Later in the year Spiræa Ulmaria forms an extremely 
dense growth, much more so than in the Shade Society. It is often almost 
pure, but mixed with it is usually some Angelica sylvestris, Cnicus palustris, 
and Rumex viridis, the first-named being locally extremely abundant. This 
is hardly a separate society, but only a light variation of the former one. 
The water-content shows a slightly higher summer average, 43 per cent. 
In these бричга Societies there are local patches, not usually very large, in 
hollows, &с., where the water-content never falls below 40 per cent., and 
# Woodhead, 1906, p. 345. + М Christy, 1897, p. 192. 
t Adamson, 1910. | 
$ The term “open ” is here used to express a less degree of shade, in opposition to the 
‘shade ” type of society. 
|| Clements, 1905, p. 821, 
