leaf is deeply lobed. It is then either a Viburnum or an Acer, 
and the fact that the leaf-margin is lobed and not finely serrate 
brings the chase down to Acer. Before going further go back 
over the key and make careful note of the particular characters 
which were used to separate this genus from the other genera 
and try to fix these in mind. This done, turn to the page indi- 
cated, where you will find a Summer Key to the Species of Acer. 
You run through this key in the same manner that you did the 
genus key. If you have been careful in your search you will 
finally stop at Acer saccharum. Once more pause and go back 
over this key and try to fix in mind the characters which were 
used to separate the various species, especially the difference 
between your tree and Acer platanoides, which it so closely 
resembles. This done, turn to the page indicated and compare 
the characters of your tree with the drawings and descriptions. 
If you are satisfied with your diagnosis, well and good. If you 
find that you are wrong, go over the keys again and find wherein 
you were led astray. 
Before you leave the tree take a sample of leaf properly 
labeled which you can press between the pages of an old magazine 
and save for future reference. Do this with other trees which 
you may find and when you get home lay them out side by side 
so that the labels will not show and compare them. A few trials 
of this kind will serve to form a mental picture of each jeaf 
which you will remember. 
A very helpful practice for the beginner is that of making 
keys based upon various characters. Practice keys of this kind 
will bring out the differences and likenesses of trees as will no 
other means, and characters which have hitherto escaped the eye 
will be prominently brought forward. Nor should the student 
take his characters from books, but rather should he go to the 
woods and get his knowledge first hand. 
It is thardly necessary to state that the key is a valuable 
crutch while learning to walk, but once the leg is strong enough 
to bear the weight it should be discarded, lest it become a burden. 
A key has for its main object the guidance of the student through 
the preliminary steps leading to a more intimate knowledge of the 
trees. When once he knows a tree, instinctively, because of long 
acquaintance with it, just as he knows people, then the need for 
a key will have ceased. 
