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366 NEW PUBLICATIONS.
cially in mitigating the winter, comparatively tender plants flourish in
the open air throughout the year. A warm winter is an essential con-
dition for the existence of tender" plants viiih. pet'ennial stems. (So far
very good.) In the neighbourhood of London, on the other hand, the
semi-spontaneous exotic plants which belong to the vegetation of cli-
mates with a higher mean temperature are necessarily annuals. (It does
not follow from climatic causes that they should be annuals, so that
this sentence placed in connection with the preceding one, conveys a
wrong impression.) Many of them are more abundant in some years
than in others, a warm spring being essential to allow them to reach
maturity before the first frosts. Provided that the summer heat is suffi-
cient to allow them to ripen their seeds, annuals are capable of a more
extended northern duration than perennials. (Sentence very obscure.)
With regard to perennials, the following remarks may be quoted from
Mr. Baker :— " In general terms, the polar limit of species liable to be
killed by frost runs across Europe from N.W. to S.E. diagonally with
the parallels of latitude ; and to sum up in a single comprehensive
phrase the relations of the British to the Continental flora, we may say
that the north limits of the plants as regulated by temperature radiate
from our island like the spokes of a wheel from the axis." (By restrict-
ing this comparison to perennials it is spoilt, and conveys quite a wrong
impression. It is true only when applied to the British flora as a
whole. It is annuals that furnish the ascending spokes of the wheel,
the evergreen perenrtials the lowest descending spokes, the biennials
and decicluoits-leaved perennials the intermediate ones.) P, xxxix.
Upwards of three hundred closely printed pages are occupied by the
list of species, with a detailed account of their dispersion through the
seven drainage districts. A full list of special stations is given for all
but the common ones, and especial pains is taken under this head with
the flora, present and past, of the metropolitan tract. Under each
species are given any old n^mes under which it has been recorded, as a
Middlesex plant, and the date of the first notice of its occurrence. Of
the care with which the history of the species is traced, and with which
the records of their occurrence have been gathered together, we shall
best give an idea by an extract.
48. Sisymbrium Ieio, L. London Rocket.
Irio IcBvis apu/a, Col. (Merrett). Erysimum latifolium Neapolitanum, Park.
(Ray). Erysimum latifolium majus (jlahrum, C. B. P. (Morisoii). Cyb. Brit,
i. 150 ; iii. 38-i ; Coiiip. 102. Curt. F. L. f. 5 (drawn from a Lonclo)i plant).