If you can find a tree with three or four strong spreading branches, the problem of erecting a house is not a difficult one. If there are four straight trees the proper distance apart, it is a comparatively simple work to erect your house between their trunks, high enough to be out of reach of River Rats; but trees, as a rule, do not regulate their growth to suit any set of boys, and the boys must use their ingenuity to adapt their houses to the forms and growth of the available trees. [Illustration: Tree-top House. 6 × 10 feet, 35 feet from ground to floor.] First choose your location, and see that it is a desirable one to all the club members; then, if there are any lofty trees at The Desired Spot you will certainly find an opportunity for a four-tree, three-tree, two-tree, or one-tree house. The tree or trees for the purpose must be so tall, that when the bottom ladder is pulled up the house will be out of reach of unwelcome callers, and big enough to prevent the wind from so swaying the house as to give a feeling of insecurity. A Two-Tree House. Let us suppose that there are only two trees in the proper location which fulfil the requirements, and that these are tall pines with no branches of any importance below their feather-duster-like tops. This presents one of the most difficult problems to solve; but when you know how, you can erect a most enchanting “crow’s-nest” away up the tall trunks, where the fresh breeze blows over the tops of the smaller trees, and where a good view can be had of the surrounding country, and the enemy, if there be one, may be seen while yet a long distance off, giving ample time to the club members to pull up the ground ladder and place themselves in position to laugh at the foe. [Illustration: FIG. 2.--King Posts and Corbel.] How To Start. With an accomplished woodsman the whole edifice may be erected with the use of no other tool than an axe; but, as a rule, the more tools you have at your disposal the better you can do your work. If you possess a tape-line, measure the distance with it between the two tree-trunks. If you have no tape but have a two-foot ruler, make yourself a longer measure by marking off the feet and half-feet upon a ten or twelve-foot pole, and use it to measure between the trees. If, however, you have neither, use your legs and pace the distance, and then cut two long, strong poles, and see that they are long enough to span the distance between the trees, leaving plenty of wood to project beyond each tree. Flatten one side of each pole as shown in the diagram B, B, Fig. 1. Next, select a sound log, a foot or so in diameter, quarter it, and make four A Blocks, each about two feet long. See A, A, and A′, Fig. 1.