The student should have some idea of the terms _genus_, _species_ and
_variety_, although they are not capable of exact definition.
A _species_, or kind, is in botany the unit of classification. It embraces
all such individuals as may have originated in a common stock. Such
individuals bear an essential resemblance to each other, as well as to
their common parent in all their parts. E.g., the Cinnamon fern is a kind
or species of fern with the fronds evidently of one kind, and of a common
origin, and all producing individuals of their own kind by their spores or
rootstocks. When such individuals differ perceptibly from the type in the
shape of the pinnæ, or the cutting of the fronds, we have _varieties_ as
_frondòsum_, _incìsum_, etc. Or if the difference is less striking the
word _form_ is used instead of variety, but in any given case opinions may
differ in respect to the more fitting term.
A _genus_ is an assemblage of species closely related to each other, and
having more points of resemblance than of difference; e.g., the royal fern,
the cinnamon fern, and the interrupted fern are alike in having similar
spore cases borne in a somewhat similar manner on the fronds, and forming
the genus _Osmunda_. In like manner certain members of the clover
group--red, white, yellow, etc., make up the genus _Trifolium_.
Thus individuals are grouped into species and species are associated into
genera, and the two groups are united to give each fern or plant its true
name, the generic name being qualified by that of the species; as in the
cinnamon fern _Osmúnda_ (genus), _cinnamòmea_ (species).