When you have reached this stage in your collecting you will feel that you need some book to guide you and act as a check on your studies. All the books mentioned in the lists in this book are useful for beginners. If you find a book which pretends to take the place of the plants themselves, you would better throw your money away than buy it. Instead of helping it will hinder your progress. You will find in beginners' botanies what is known as a "key." Now, a key is obviously to unlock something with. If you had a door key which turned with difficulty, or fitted the lock imperfectly you would be sure to have it repaired or get a more modern one. Some of the old botanical keys seem to be rusty and it is difficult to use them. Choose the key that works most easily. In making a key for classifying plants one begins by dividing the whole vegetable kingdom into two big departments, thus: A. Plants which never have flowers. AA. Plants which do have flowers. As your specimens are all of the flowering kind we shall for the present forget all about the others and begin to divide our big group AA into smaller groups. This is how it is done: AA. Flowering plants. B. Flowers not showy, seeds in cones (usually), leaves needle--or scale-like, evergreen (usually). BB. Flowers showy, seeds not in cones, leaves of various shapes, deciduous (usually). You will see that in dividing a group it is important that A is just the opposite of AA, and B is just the opposite of BB, and that the place to look for BB is just the same distance over from the margin of the page as B although it may not be on the same page, if there are a great many divisions under B. These little things make the key easier to use than the old-fashioned ones were. Some people still use botanical keys as mental gymnastics but I do not believe in that. After all you are studying plants not keys. You will want to go back to the group we called A, for to the non-flowering plants belong the lovely ferns which must certainly grace your collection. This is a delightful group to study and it is possible with a reasonable amount of persistence and by exchanging with fern collectors in other parts of the country to get a very nearly if not quite, complete collection of native forms. Only one hundred and sixty-five of the four thousand species of ferns are native to the United States. Such a collection should be very valuable.