To understand what sort of trees they were from which he got his inspiration, you must look, not at an average English wood, perpetually thinned out as the trees arrive at middle age.  Still less must you look at the pines, oaks, beeches, of an English park, where each tree has had space to develop itself freely into a more or less rounded form.  You must not even look at the tropic forests.  For there, from the immense diversity of forms, twenty varieties of tree will grow beneath each other, forming a close-packed heap of boughs and leaves, from the ground to a hundred feet and more aloft.

You should look at the North American forests of social trees—­ especially of pines and firs, where trees of one species, crowded together, and competing with equal advantages for the air and light, form themselves into one wilderness of straight smooth shafts, surmounted by a flat sheet of foliage, held up by boughs like the ribs of a groined roof, while underneath the ground is bare as a cathedral floor.

You all know, surely, the Hemlock spruce of America; which, while growing by itself in open ground, is the most wilful and fantastic, as well as the most graceful, of all the firs; imitating the shape, not of its kindred, but of an enormous tuft of fern.

Yet if you look at the same tree, when it has struggled long for life from its youth amid other trees of its own kind and its own age, you find that the lower boughs have died off from want of light, leaving not a scar behind.  The upper boughs have reached at once the light and their natural term of years.  They are content to live, and little more.  The central trunk no longer sends up each year a fresh perpendicular shoot to aspire above the rest, but, as weary of struggling ambition as they are, is content to become more and more their equal as the years pass by.  And this is a law of social forest trees, which you must bear in mind whenever I speak of the influence of tree-forms on Gothic architecture.

Such forms as these are rare enough in Europe now.

I never understood how possible, how common they must have been in medieval Europe, till I saw in the forest of Fontainebleau a few oaks, like the oak of Charlemagne and the Bouquet du Roi, at whose age I dare not guess, but whose size and shape showed them to have once formed part of a continuous wood, the like whereof remains not in these isles—­perhaps not east of the Carpathian mountains.  In them a clear shaft of at least sixty, it may be eighty feet, carries a flat head of boughs, each in itself a tree.  In such a grove, I thought, the heathen Gaul, even the heathen Frank, worshipped beneath “trees of God.”  Such trees, I thought, centuries after, inspired the genius of every builder of Gothic aisles and roofs.