Another tree with warty bark is the sweet gum. The negroes of the South call the tree " alligator wood," because the lower part of the trunk is broken by furrows and cross-furrows into horny plates like the skin of an alligator. From the red-brown trunk up into the grey branches, there is a change in the character of the bark. The fissures usually run lengthwise, and the bark rises in thin ridges on each side of the fissure. These ridges become thin as knife blades on the smaller twigs, which also have a sprinkling of small warts.
A sweet gum is very rugged looking in the dead of winter, with its warts and ridges break ing out on each limb. We know it by this sign alone, but are doubly sure when we see the seed balls dangling from the twigs. The sycamore, blotched with white on trunk and !imb, also car ries a load of dangling seed balls throughout the winter. There is no danger of confusing these two trees, for the bark of each is so dis tinct.
A little tree with alligator skin bark grows North and South, and chiefly in the eastern half of the country. This is the flowering dogwood, whose grey bark breaks into small squarish plates. There is no such ruggedness in its trunk as there is in the sweet gum's, for it is always a little tree, and the bark corresponds in its checking to the tree's size. When we see this peculiar type of bark in the winter woods we may look also for little flattened, box-like flower buds, each en closed in four scales. We shall also find the twigs set opposite, and with these three signs be sure we know the tree.
A little tree, no larger in girth than the dog wood, but often taller, has bark that strips and loosens somewhat as the bark of the shagbark hickory does. This is the hop hornbeam, one of the ironwoods. Its bark strips are always thin and narrow, no matter how old the tree becomes. It is never as loose upon the trunk as the shag bark's. The great buds and stout twigs of the hickory are entirely different from the slender spray and the very small buds this ironwood wears in winter. We may find on these twigs
some remnant of the hop-like seed clusters which give this little tree its name, hop hornbeam. In side its shaggy bark the lumbermen find wood so hard that it is very difficult to work, and when made into tools it lasts almost forever.
When we have learned to know at sight a dozen trees by their bark alone, we are ready to go further. A great many trees with furrowed bark like chestnuts and elms and maples, are not so distinct as those already learned, and we must study the tree's form, its winter buds, the arrangement of these buds, and the shape of the leaf scars in connection with the bark, in order to be sure we know the tree's name. The chestnut from which we gathered so many nuts last fall, and whose furrowed trunk we saw. at every visit, we come to know through this fa miliarity. The trunks of other chestnut trees look like this one, and though we may not know just how we do it, we have added the chestnut to the list of trees we recognise by their bark alone. The sugar maples which we tap in spring for their sugary sap, have dark, furrowed bark, not very distinctive. And yet, by going from tree to tree, emptying the sap pails, we gradually learn to recognise the bark of the sugar maple, and add it to our growing list.
Trees do not change their clothes, and they do not move away. Day after day, if we use our eyes and notice what is going on in the tree tops, as the seasons follow each other, we come to know our trees by name; we recognise them in winter by their bark, and by the framework of their tops, in summer by leaves and flowers, in autumn by their changing colour and by their fruits. It is not hard work for those who love trees. It is like getting acquainted with other neighbours whom we are glad to count among our friends.