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 with perennial 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 sufti- 
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 iu 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 perennials the lowest descending spokes, the diennials 
and deciduous-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 names 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 Inro, L. London Rock 
Trio levis apula, Col. (Merrett). Bryans latifolium Neapolitanum, Park. 
(Ray). Erysimum latifolium majus eines . B. P. (Morison). Cyb. Brit. 
i. 150; iii. 384; Comp. 102. Curt. F. L. f. 5 (drawn from a London plant). 
