Читать книгу Trees of the Northern United States - A. C. Apgar - Страница 15

Table of Contents

Method of Using the Key.

First read all the statements following the stars (*) at the beginning of the Key; decide which one of the statements best suits the specimen you have. At the end of the chosen one there is a letter in parenthesis ( ). Somewhere below, this letter is used two or more times. Read carefully all the statements following this letter; at the end of the one which most nearly states the facts about your specimen, you will again be directed by a letter to another part of the Key. Continue this process till, instead of a letter, there is a number and name. The name is that of the genus, and forms the first part of the scientific name of the plant. Turn to the descriptive part of the book, where this number, in regular order, is found. Here descriptions of the species of the genus are given. If there are many species, another Key will lead to the species. While the illustrations are intended to represent characteristic specimens, too much dependence must not be placed upon them; the leaves even of the same plant vary considerably, and the different varieties, especially of a cultivated plant, vary widely. Read the whole description before deciding.

The fractions beside the figures indicate the scale of the drawing as compared with the natural size of the part: 1/1 indicates natural size; 2/1, that the drawing is twice the length of the object; ¼, that the drawing is one fourth the length of the object, etc.

In the description of leaves the dimensions given refer to the blade.

KEY TO THE GENERA OF TREES.