5. How plants are named. Whenever many objects are to be studied and compared, it is necessary to have some convenient system of naming them and some method of expressing the various degrees of resemblance and difference which may be found. The number of plants which botanists now have to deal with is estimated at about one hundred and seventy-five thousand. Only a small proportion of these plants have names in English, German, French, Italian, or other modern tongue; and even if they had, it would be an intolerable burden for students who need to consult the writings of foreign botanists to learn as many names for each plant as there are modern languages. Fortunately it has been agreed among botanists that each kind of plant shall have one botanical name, and only one, in all countries.1 This name is Latin or of Latin form for the reason that the earlier botanical writings were in that language; and as educated people of whatever nationality are supposed to have some acquaintance with Latin, nothing could be more convenient for botanical purposes. For popular use, however, popular names are required and will be used chiefly, therefore, throughout the coarse print of the following pages.

1 Such, at least, is the botanical ideal. It is not always realized in practice. But mistakes and differences of opinion are surely to be expected in the naming of such a vast number of objects. Yet after all the actual confusion produced is comparatively slight, while the ideal pursued has advanced the science wonderfully.