202 
POPULAR SCIENCE REVIEW. 
is very doubtful wbether it is indigenous in England. It is, 
however, a native of many parts of Europe. The root owes 
its quahties to the presence of a volatile oil which is dissipated 
by drying. There is no difference between the wild and cul- 
tivated plant, except that the root of the former is smaller and 
more stringy if it happens to grow in a poor soil ; but if the 
soil should be moist and rich in which it is found, then the 
root of the wild plant is equally good. 
We would recommend our readers, if they have leisure, to 
prosecute this inquiry, as it will be found most interesting in 
connection with the early periods of human history. It is also 
an important inquiry, because it has a direct bearing on those 
formidable questions as to the Origin of Species,^'’ as to the 
amount of variability of which s]3ecies are susceptible, and the 
causes by which that variability is produced ; and lastly, as to 
the geological epoch at which existing species were first intro- 
duced, questions which the best naturalists find it so difficult 
to answer, and which will only be understood when natural 
history is much more advanced, and the links discovered 
which unite the present plant forms with those which have 
preceded them. 
We have historical evidence that existing species have not 
varied for several thousand years, and the reason is plain 
enough, because the external cmcumstances in which they have 
been placed have not varied. For all practical purposes, 
therefore, the characters on which species are found may be 
assumed to be constant ; and a minute and careful description 
of a plant will suffice, not only for the present, but for many 
succeeding generations of naturalists. But we have no war- 
rant from nature to assume that such specific, or even generic, 
characteristics either have, or will continue to be, permanent 
for an unlimited period of time, that they will survive all future 
changes in the physicial geography of the planetary surface. 
We know that great changes may be efiected in a brief space 
of time in the organization of plants by cultivation ; and why 
should not an organic change be brought about in plants when 
their external circumstances are altered by nature in the course 
of ages ? This world, what is it but a great and ancient theatre 
where the scenery of life is ever changing ? Look at that ma- 
jestic and venerable tree ; its present form appears to be fixed, 
yet that very form is in reality as fleeting and evanescent as all 
the other forms through which that tree has passed from its 
first life movement in the seed ; and what is true of that tree, 
which is a part of nature, is true of the whole of nature, the 
present appearance of nature now is no more unalterable than 
at any other geological e^Doch. It is the last of the many 
phases of creation, and equally fleeting with all the others. 
