for the advance of Botany. H7 
occur. Perhaps we may be allowed to suspect some analogy between 
the primitive forms of crystals, and those normal or typical forms 
which may be assigned to different species of plants, by the appli- 
cation of such rules of morphology as already appear to a certain ex- 
tent satisfactorily established, viz. the partial suppression or com- 
plete abortion of particular organs, and the adhesion of others. Al- 
though no precise laws have hitherto been discovered in botany, 
which assign the limits of variation to a given species, some approxi- 
mation to them might possibly be expected, by attending more strict- 
ly than seems to have been customary to the principles of analogi- 
cal reasoning. Thus, when we find the admitted varieties of one 
species ranging through certain peculiarities of structure, it is rea- 
sonable to suppose, that if we now find two other individuals of 
the same genus, which do not differ more, or so much from each 
other as the former two, then these ought also to be considered as 
varieties of a single species. In the determination of species, our 
most eminent botanists seem frequently to be acting against their 
own judgment, and compelled to describe as distinct what they 
have little or no doubt themselves, ought to be considered as identi- 
cal. Hence they are perpetually qualifying their descriptions with 
such phrases as these, " Priori nimis affinis," " vix et ne vix dis- 
tincta," and even after this a third species is still described as 
" duabus prioribus exacte intermedia !" It is perhaps extremely 
difficult to form any decided opinion about the limitation of species, 
and we find some persons who, instead of wishing to multiply them 
beyond their due limits, are inclined to run to the opposite extreme, 
and believe that there is no such thing as distinct species at all ; a 
clear proof again that we are in want of multiplied experiments, 
undertaken by careful and scientific observers. But we shall never 
make any progress towards solving the problem, if we continue dis- 
satisfied with the positive results of experiments, merely because 
they happen to militate against our preconceived notions ; and 
-though a proper degree of caution ought always most unquestionably 
to be exercised, before we admit even the most positive evidence in 
favour of a new and startling fact, yet there can be very little value 
assigned to any mere assertions which may be made contradictory 
of such a fact, even though they should be partially supported by 
the negative results of direct experiment. Although several years 
have passed since Mr Herbert proved by experiment that numerous 
varieties of Primrose, Cowslip, Oxlip, and Polyanthus, might origi- 
nate from the seeds of a single plant, agreeably to the opinion of 
Linnaeus, who considered them all to be mere varieties of the same 
