With the incoming of the nineteenth century, botany took a rapid start. It ceased to be a mere handmaid to the study of medicine. Chemistry, geography, teleology, and indeed the chief foundations of biology had become closely interwoven with botanical studies; and thus the progress of botany through the century has to be viewed from many standpoints. In classification, what is known as the natural system has replaced the sexual. Plants are grouped according to their apparent relationships. Those resembling in general character the Rose form the order _Rosaceæ_; the Lily, _Liliaceæ_. Sometimes, however, a striking characteristic is adopted for the family name, as _Compositæ_, or compound flower, for the daisy and aster-flowered plants; _Umbelliferæ_, or umbel-flowering, as in carrot or parsley; _Leguminosæ_, having the seed vessels as legumes, like peas and beans. [Illustration: HEAD OF WHITE CLOVER, WITH A BRANCH FROM THE CENTRE.] Classification has, however, derived much assistance from a wholly new branch of the science known as Morphology. This teaches that all parts of plants are modifications of other parts. What Nature may have intended to be a leaf may become a stem; the outer series of floral envelopes, or calyx, may become petals; petals may become stamens; and even pistils may become leaves, or even branches. The green rose of the florists is a case in which the leaves that should have been changed into petals to form a perfect rose flower have persisted in continuing green leaves, though masquerading as petals; and it is not unusual to find in the rose cases where the pistils have reverted to their original destination as the analogue of branches, and have started a growth from the centre of the flower. So in an orange, the carpels, or divisions, are metamorphosed primary leaves. Two series of five each make the ten divisions. Sometimes the axis starts to make another growth, as noted in the rose, but does not get far before it is arrested, and then we have a small orange inside a larger one, as in the navel orange. Just the reverse occurs sometimes. The lower series is suppressed, and only the upper one develops to a fruiting stage, when the small red oranges known as the Tangerines are the results. Illustrations of these transformations of one organ to another are frequent if we look for them. The annexed illustration shows a condition of the white clover, which, instead of the usual round head, has started on as a raceme or spike. These wanderings from general forms were formerly regarded as monsters, of no particular use to the botanical student, but are now welcomed as guiding stars to the central features of Morphology. The importance of this branch of botany, in connection with classification, can readily be seen.