2 
“—T ae sas anid 
a a oe 
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23 
country, and on their adaptability to the conditions of existence in 
it. We cannot regard any species as having originated in Britain, 
though certain species present varieties not yet met with in other 
countries. Hence the question of what should be included within 
the limits of the British Flora is one that cannot be settled on any 
hard and fast lines, but must be recognised as open to consider- 
able differences of opinion. Probably all floras are slowly receiving 
additions independent of human agency. 
By noting carefully the first appearance in a locality of plants 
previously unknown in it, and by endeavouring to trace out the 
mode of their introduction, whether by man, consciously or un- 
consciously, or by agencies independent of him, we may aid in 
arriving at a knowledge of the laws that regulate the development 
of the flora of that locality, and may be able to apply these to 
floras in the wider range. 
We may also learn something of the laws that enable certain 
forms to prevail in the struggle for existence, if we observe 
which of the new-comers can hold their ground or increase, 
and note specially the conditions under which they do so; and 
we may also be able to detect the causes whereby others die 
out and disappear even under the most apparently favourable cir- 
cumstances. It is hoped that this list may be of some interest in 
this direction. 
An analysis of the subjoined list will show a considerable addi- 
tion to the “casuals” recorded in Dickie’s “Guide.” A few of 
these are not very rare, and are striking species; but most of 
them are, as might be supposed, merely sporadic; and only a 
small proportion seem able or likely to establish themselves. Most 
die out in a year or two. 
A moderately careful scrutiny will show that the casuals noted 
are divisible into a few great groups in respect to their introduction 
into our district. These groups are :— 
1, Trees or shrubs intentionally introduced into plantations. 
These may not spread, or may produce ripe seeds, which 
may be dispersed by wind (poplars and willows), or by 
birds (service-tree, &c.) . 
2. Introduced as part of, or with, field crops—beans, tares, grasses. 
3. Grown in gardens or pleasure grounds for beauty, or as culinary 
herbs, thence spreading by stolons or seeds, or thrown out 
among garden weeds or rubbish. 
