PRINCIPLES OF FLORICULTURE. 
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especially the anthers, which appear to require the stimulus of 
more heat than any other part of the plant; and the consequence 
is, that the same parts which become stamens and anthers in 
Mexico, cannot get beyond the state of petals in this country. It 
is only, however, when highly bred that the Dahlia becomes so 
double; for if it is left year after year in the ground all the 
winter, the number of petals gradually diminishes ; and parts of 
fructification, though not very fertile, in consequence of the want 
of stimulus, come in their stead. If, however, the very same 
plants have their tubers taken up during the winter, and are other¬ 
wise restored to careful culture, they again become double, though 
some of the reasons are too obscure for our observation. 
Plants which thus admit of extensive variations in their growth 
or flowering, are always such as have the principle of life very 
vigorous in them, and are always very highly sensitive to physical 
changes of situation and treatment. The Dahlia and the Rose 
are among the most remarkable instances of this ; and, though 
there are many natural distinctions, and innumerable cultivated 
varieties of both, it is probable that the wdiole of each are 
originally of one species. The men who deal in the systematic 
arrangement and nomenclature of plants, appear, however, to 
have very confused notions as to what constitutes a natural 
species of plant and what does not. Hence, in both the Dahlia 
and the Rose, many natural species are distinguished by them, 
of which the distinctions are brought about by geographical 
and other local causes ; and therefore, the whole of each, how 
different soever in appearance, are really of one ph} r siological 
species. 
If we had the plants, and the circumstances to which their 
variety is owing, wholly within the scope of our observation, we 
should, in all probability, find that any one of these many 
varieties can be converted into any other by treatment; only 
much of that treatment lies without the range of our observation. 
The third object to which the breeder of plants, and more 
especially of flowers, directs his attention, is the procuring of new 
varieties, whether in the general appearance and habit of the 
plant, or in the qualities of the flowers. This is a more compli¬ 
cated matter than the mere increase of flowering, or the size of 
the flower and the number of its petals; and almost all that is 
known concerning it consists of the results of experiments, which 
VOL. II. NO. VIIT. 
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