in. INTRODUCED SPECIES. 89 



opposing an opinion that is in itself correct. In reliance 

 on the general Floras of Britain, and on the statements 

 of several local observers, Stratiotes aloides was treated in 

 the second volume of this work as an unquestioned native 

 of Britain. It is enumerated as such also for Holland in 

 the Disquisition of Dr. Miquel. But M. De CandoUe, 

 with much probability, considers this tropical-seeming 

 plant as having been originally brought from Southern 

 Asia. Now, in this instance, would the Author of the 

 Geographie allow anj^ force to the following st3de of argu- 

 ment ? — Recorded also in Holland ; therefore a true 

 native of Britain. Or, converselj', Recorded also in 

 Britain ; therefore a true native of Holland. 



These two examples may have their usefulness in sug- 

 gesting to readers, who are less conversant in such mat- 

 ters, the need of much caution in deciding upon the 

 condition of a species in one country, by examining the 

 records of its condition in another ; especially so if the 

 two countries are disjoined by the present seas. In re- 

 gard to the vegetation of England, the two facts (first) of 

 the seeming nativity of a species on the Continent, and 

 (second) its seeming non-nativity in England, lead toge- 

 ther to an important problem in geographical botany. 

 To take the first datum as a negation of the second da- 

 tum, is surely a solution of the problem more light than 

 logical ? 



A third kind of evidence, to which M. De Candolle 

 attaches considerable value, is that derived from the 

 terms in which Authors have described the usual situa- 

 tions for the species, whether agrestal, viatical, pratal, 

 &c. If he finds plants only described as occurring 

 " inter segetes," or in other agrestal situations, he deems 

 them not shown to be native or even properly naturalised 

 species. The more they are recorded beyond these and 



VOL. IV. N 



