ADDITIONAL LIST. 465 
opinion about them. As examples, we may take Geranium 
pheum, Spirea salicifolia, Saxifraga umbrosa, Lonicera Xylos- 
teum, Valeriana rubra and Galanthus nivalis. On the contrary, 
at the other extremity of a series, some of the aliens are so very 
local, or so uncertain in persistence at any given place, as to be 
scarcely separable from the next group. 
3. Casuals.—These together make a wide range of plants 
between the two extremes of the group. Some few of them are 
met with almost as frequently as some of the colonists; being 
now hardly separable from the latter, unless on the ground of 
only recent notice, that is, by the absence of records for them 
in the books of past generations. Veronica Buxbauwmii was 
unnoticed in the ‘English Flora’ of Smith, under date in 1824. 
Now, it is seen so frequently on arable land, as to demand pro- 
motion to the quasi-indigenous rank of colonist. Midway between 
1824 and 1869, it might have passed as a casual, occasionally 
introduced among clover or other agricultural seeds. Perhaps 
others of the plauts, which remain still to be curtly noticed here 
as casuals only, may be gradually advancing now to the higher 
predial grade. It can scarcely be doubted that Galinsoga parvi- 
flora, Crepis setosa, Cynosurus echinatus, Bromus arvensis, with 
some other weeds of cultivated ground, are now met with more 
plentifully than was the case with them not many years back. 
As far as it can be applied, the best test to separate the colonists 
from the casuals, is that of regular self-maintenance in this 
country by seed ripened here, without the necessity of renewal 
through fresh importation. From other aliens, the casuals are to 
be distinguished chiefly by less persistence in their localities; 
a distinction often turning on their physiological character of 
annuals or perennials. 
Passing to the other extreme of the series, we reach plants 
which have been so rarely seen, or have proved so transitory in 
any given place, that it is barely justifiable to enumerate them 
among things only casually quasi-british, Through such plants, 
the present group gradually merges into that of extinct plants; 
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