the genera of umbelliferous plants, for which purpose the latter deemed the part in question very important. But according to the laws which Linnæus had laid down, the parts of the flower and fruit alone were to afford generic characters, and the most sound botanists have ever since kept to this rule, with infinite advantage over less correct ones, however ready to derive ideas respecting the natural habit, and secondary characters, of a genus, not only from the inflorescence and bracteas, but even from the leaves, stipulas, or other parts. Linnæus and Artedi, therefore, were obliged to consider the involucra and involucella, the former accompanying the general and the latter the partial umbels, as a sort of calyx, and the umbel altogether as one aggregate flower, composed of florets united by a common radiated receptacle. Consequently a cyme must be considered in the same light; nor are reasons wanting in support of this hypothesis, which we shall consider after having first explained all the parts of fructification.
In Euphorbia, however, the term bractea
