Passing on to the leaves, we may note the importance of obtaining in every case the root-leaves of each species. These are often very different in form from the stem-leaves, as in such species as the harebell (_Campanula rotundifolia_), _Pimpinella saxifraga_, the earth-nut (_Bunium flexuosum_), and many more; in some instances, as in the Jersey bugloss (_Echium plantagineum_), they at once characterize the species. Still more important are these lower leaves in the case of water-plants: in the arrowhead (_Sagittaria_), for example, they are narrow, and resemble those of the bur-reed (_Sparganium_); and in the water plantain (_Alisma plantago_), the submerged leaves are equally different from those which rise out of the water. This difference is still more noticeable in the case of the aquatic _Ranunculi_, where a knowledge of the submerged leaves is essential to the discrimination of the various forms or species. Where practicable, the whole plant should be collected for the herbarium; but when, from its size, this cannot be accomplished, leaves from the root, the centre of the main stem, and the lateral branches, should be taken. As to the stem itself, that must be represented: in the _Rubi_, indeed, it is essential. "To judge properly of a bramble from a preserved specimen," says Professor Babington, "we require a piece of the middle of the stem with more than one leaf; the base and tip of the stem are also desirable, likewise a piece of the old stem with the flowering shoot attached to it; the panicle with flowers, and the fruit. We likewise want to know the direction of the stem throughout, of the leaflets, and of the calyx; also the shape of the petals and the colour of the styles: a note of these should be made when the specimen is gathered." Passing on to the flowers, we shall find it necessary to represent them in almost every stage, from the bud to the perfecting of the fruit. It is of course in most cases possible to select an example in such a state as to show upon the same plant buds, flowers, and fruits; but where this is not the case, each of these particulars must be supplemented by additional specimens. The turn which botanical investigation has recently taken towards the study of the phenomena connected with fertilization has given the collector another subject to which his attention may be profitably directed. It has been observed that in some plants the stamens are developed before the pistils; in others, the pistils are matured before the stamens; while in yet a third set, stamens and pistils are simultaneously perfected. These three groups of plants are termed respectively protandrous, protogynous, and cynacmic, and a very little observation will show that examples of each are sufficiently common.