THE PRIMROSE AND OXLIP IN ESSEX. 121
agents ; but it should also be remembered that both plants have
enemies in birds. Sparrows, in particular, will feed on the ovules of
primroses as soon as they are developed and will destroy an
incredible number of blooms. Still, after all these allowances, there
is a fair proportion of seed ripened ; it is not, therefore, to the lack
of seed that paucity of plants can be traced.
Taking into account the limited range of the Bardfield Oxlip in
Britain, it can hardly be regarded as an aggressive species. At one
place along the southern limit we have mentioned the area extends
as a tongue into the northern area of the primrose. This is at Box-
ted Wood, a little south of Great Saling. In the neighbourhood of
the wood the primrose grows very sparingly, but within the wood its
place is monopolised by the oxlips, and they can there be counted
literally by thousands. The explanation here is obvious that the
wood should be regarded as an outlier of the oxlip area which has
not succumbed to agricultural interference.
The primrose cannot be regarded otherwise than as a diminish-
ing quantity in North-western Essex, which is partly due, as with the
Bardfield Oxlip, to agricultural and other influences, but more
particularly, as it would seem, to the want of agents for the dissemi-
nation of the seeds. This is the only rational explanation for the
narrow border to which we have adverted as being nearly destitute
of both species. Primroses are common enough south of that
border.
Why the primrose should be so exceedingly rare or absent in the
area inhabited by the oxlip, is not easy to say. Darwin says that its
range on the Continent "differs somewhat from that of the cowslip
and primrose, and it inhabits some districts where neither of these
species live." Although, as we have observed, the presence of one
plant is not directly inimical to the other, there is doubtless some
indirect manner in which Primula elatior injures P. vulgaris.
Darwin made many experiments on the cross-fertilisation of these
two species and of Primula veris, all nearly allied (see "Different
Forms of Flowers in Plants of the same Species"). Unfortunately
these experiments do not help us to a solution ; but incidentally
Darwin touches upon a problem which may be placed alongside of
our difficulty. In treating of the Common Oxlip, which is a hybrid
between P. veris and P. vulgaris, and is in nowise to be confounded
with the Bardfield Oxlip, he mentions the singularity of this hybrid
being frequently found in some districts and rarely in others, and
I