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Johnston^ s Flora of Bei^nsoick upon Tweed, 235 



The district, whose vegetable productions he professes to 

 examine, contains every variety of soil, whether inland or on 

 the sea shore; and is remarkably distinguished also for the 

 variety of its stratification. The catalogue is very properly 

 prefaced with an account of the geology of the neighbour- 

 hood, drawn up by a friend of the author, who has justly 

 impressed upon his readers, both by precept and example, 

 the importance of remarking the geological relations of plants. 

 Up to a late period, the compilers of Floras have thought 

 it of more consequence to add a species, than to ascertain 

 its relation to the locality in which it was found ; yet every 

 addition to the Flora of a country throws some light on the 

 laws of vegetable distribution. It suggests the questions 

 whether it be indigenous and coeval with the soil; or if 

 introduced, by what means that has been effected. Whether 

 arts or commerce, agriculture or manufactures, superstition 

 or medicine, has brought it; or, which is frequently the case, 

 whether the altered state of the earth's surface has not af- 

 forded to Nature, by her ordinary laws, increased means of 

 diffusion. In the days of Gesner, jPumaria ofiicinahs was a 

 very rare plant in the fields of southern Europe, and sup- 

 posed to have come from the East ; now it is the commonest 

 weed in corn fields and gardens, from Greece to Lapland. 

 Again, as plants approach the limits of their range, it is often 

 curious to enquire what soils or rocks they prefer. Many 

 south country species, without showing any particular attach- 

 ment in places where they abound, become choice as they 

 approach their northern boundary. Some terminate their 

 range on chalk ; others on mountain limestone, or red sand- 

 stone, or the sea shore. Some, which with us affect the 

 driest soil, occur, in southern latitudes, in moist ones, as iinum 

 catharticum. On the contrary, plants coming to us (so to 

 speak) from the north, what strata and soils do they prefer 

 or reject? how are the moisture, the temperature, the 

 isothermal range, compensated for, when plants reach more 

 southern parallels ? Z)aphne ilfezereum may safely be pro- 

 nounced not to' be indigenous ; because its head quarters being 

 in the subalpine regions of the north, and its locality in 

 England being in the chalk woods of Hampshire, according 

 to Miller, it is contrary to all our experience of compensation. 

 What is there, again, in the nature of some plants that should 

 dispose them to be vagabonds all over the earth, while others 

 are limited to a single spot ? It is very important, also, that 

 botanists should observe the negative list of particular places, 

 as well as the positive. For instance, it is remarkable that 

 ^'nthemis Cotula (stinking May-weed) should not be found 



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