The Elm is generally subdivided into several equal branches, diverging from a common centre at a small distance above the ground. The height of this divergence depends on the condition of the tree when it was a seedling, whether it grew in a forest or in an open field; and the angle made by these branches is much wider when it obtained its growth in an isolated situation. The shape of different elms varies more than that of any other known species. It is indeed almost the only tree which may be said to exhibit more than one normal figure, setting aside those variations of form which are the natural effects of youth and age. The American Elm never displays one central shaft to which the branches are subordinate, like the English Elm; or rather, I should say, that when it has only a single shaft it is without any limbs, and is surrounded only with short and slender twigs. This leads me to speak of its normal diversities of shape, which were originally described by Mr. Emerson under several types.
THE DOME.
This is the form which the Elm seems most prone to assume when it stands from the time it was a seedling until it attains its full stature in an open space. It then shows a broad hemispherical head, formed by branches of nearly equal size, issuing chiefly from a common centre, diverging first at a small angle, and gradually spreading outward with a curve that may be traced throughout their length. A considerable number of our roadside elms are specimens more or less imperfect of this normal type.
THE VASE FORM.
One of the most admirable of these different forms is that of the vase. The base is represented by the roots of the tree as they project above the ground, making a sort of pedestal for the trunk. The neck of the vase is the trunk before it is subdivided. The middle of the vase consists of the lower part of the branches as they swell outwards with a graceful curve, then gradually diverge, until they bend over at their extremities and form the lip of the vase by a circle of terminal spray. Perfect specimens of this beautiful form are rare, but in a row or a grove of elms there are always a few individuals that approximate to this type.
THE PARASOL.
The neatest and most beautiful of these forms is the parasol. This variety is seen in those elms which have grown to their full height in the forest, and were left by the woodman in the clearing; for such is the general admiration of this tree, that great numbers of them are left in clearings in all parts of the country. The State of Maine abounds in trees of this form, sending forth almost perpendicularly a number of branches, that spread out rather suddenly at a considerable height, in the shape of an umbrella. Trees of this type have much of that grandeur which is caused by great height and small dimensions, as observed in a palm-tree. A remarkable trait in the character of the Elm is, that, unlike other trees, it seldom loses its beauty, and is often improved in shape, by growing while young in a dense assemblage. It is simply modified into a more slender shape, usually subdivided very near the ground into several branches that diverge but little until they reach the summit of the wood. Other trees, when they have grown in a dense wood, form but a single shaft, without lateral branches.
THE PLUME.
The most singular of the forms assumed by the Elm, and which cannot be regarded as of a normal character, is the plume, caused by some peculiar conditions attending its early growth. The shaft is sometimes double, but usually not divided at all, except into two or three small branches at its very summit. It is perpendicular to near three fourths of its height, and then bends over, like one of the outer branches of a normal-shaped Elm. This whole tree, whether double or single, is covered from the ground to its summit with a dense embroidery of vine-like twigs that cluster round it in all ways, often inverted, as if it were covered with a woody vine. The cause of this form seems to be the removal of the tree into an uncongenial soil, that is too scanty and innutritious to sustain a healthy growth. Yet I have seen some trees of this shape in clearings. They do not seem to be diseased, yet they are evidently in a stunted condition. One of the most remarkable of the plume elms which I have seen stands in the northern part of Danvers, near the point where the Essex Railroad crosses the Ipswich River. I have observed a similar habit of growth in some English elms, but their shaft is always perpendicular.