9. Varieties. We have seen above that among the offspring of a single plant there will be minor differences, and that among the individuals of a species the differences may be very considerable. If in the examination of a number of specimens belonging to one species, a botanist finds certain individuals possessing in common some peculiarity or set of peculiarities which distinguish them clearly from the rest, as, for example, cauliflowers in contrast with other plants of the species Brassica oleracea, he calls the individuals thus distinguished a variety, and gives it a special name. The cauliflower thus becomes Brassica oleracea variety botrytis. Or, to take an example from wild plants, there are found among the individual trees that comprise the species called Salix nigra certain ones of which the leaves instead of being curved merely at the tip, as in the majority of black willows, are "falcate" or curved throughout like a scythe blade. All the individuals having this peculiarity are accordingly regarded as forming a distinct variety, and when we wish to speak particularly of these we use the name Salix nigra variety falcata.

Cultivated varieties which are known, or supposed, to have arisen in comparatively recent times, and show only minor peculiarities, are commonly distinguished from varieties of wild plants and from certain very well-marked varieties in cultivation by being named in English, French, or some other modern language. Thus we speak of the "Baldwin" and the "Spitzenburg" varieties of apple. As subordinate kinds or subvarieties of cauliflower we have similarly the "early snowball" and the "autumn giant."

The question as to whether a certain group of individuals should be ranked as a species or as a variety is one which is often difficult to decide, and different botanists sometimes reach different conclusions. In all cases, however, a variety is understood to be a group of individuals included within a species and consequently connected with the other members of the species by a series of intermediate forms.