Sentence:  "A plant in flower, surveyed externally", may be perceived to be composed of a variety of obvious parts, such as the root, the stem, the branch, the leaf, the flower, the fruit, and perhaps the seed; and other parts less obvious, as buds, prickles, tendils, hairs, glands, &c. These, with their modifications, and all the relative circumstances which enter into the botanical description of a plant, constitute the subject of <WSD>glossology</WSD>, the details of which, involving the definition of some hundreds of terms, are here omitted; because to those conversant to them it would be of little use, and those who have them still to learn will find it more convenient to have recourse to some elementary work, where most of them are illustrated by figures. 
Meaning of the word marked with <WSD> tags:  The naming of parts of plants.