ADDITIONAL LIST. 469 
On the other side, if it be scarcely possible to trace a decided 
line of separation between errors and extinctions, or between errors 
and out-of-sight rarities, it is found equally impracticable to separate 
the errors from the casuals. A local botanist, of little botanical 
authority or experience, may report a non-british species, say, in 
Somerset or Gloucester, in Argyle or Perth. How are other 
botanists to know for certain whether he named his plant 
correctly or misnamed it? The plant may have been misnamed, 
or it may have been a rightly named casual, introduced with 
ballast or merchandize and soon extinct there. Add to such 
instances as these, the cases where the impositions of guides or 
dealers have caused temporarily planted species to be actually 
found, and their localities reported by indiscreet botanists; and 
it will be admitted that too many errors (very probably such, at 
best) must be allowed to remain in our lists of quasi-British 
plants. Still, it would be well to begin the practice of dropping 
them out of the regular lists in our General and Local Floras, by 
committing them to an Appendix list, altogether apart from the 
proper enumeration. 
6. Ambiguities—This term is sufficiently ambiguous itself to 
cover many cases which may fall more appropriately under one or 
other of the preceding heads. As here used it may be held to 
mean or include those doubtful plants which do not clearly fall 
into the other groups. The ambiguity may attach either to the 
plant itself, or to the fact of its existence wild in Britain. The 
latter case is illustrated by Hutchinsia alpina. Some ground 
has been shewn for admitting this true species among the 
plants of Britain, but the evidence in support seems incomplete 
or insufficient. The same may be held true of Jalva borealis 
aud Thesium humile, which cannot certainly be assigned to 
the category of errors, although not verified in the localities 
reported for them. Alchemilla conjuncta is a more complicated 
example. Though very similar to A. alpina, it has physiological 
or climatal peculiarities to assist in keeping it apart, so that 
as yet Professor Babington appears to have been quite warranted 
