The excavated pits must be well drained, and filling the bottom of the pit with rubble is a good plan. The further the tree can be planted from the kerb the better, so as not only to give it a larger body of soil, but to lessen the risk of killing the tree by the pollution of the ground with gas from a defective main, and also excess of moisture from the channel gutters. The distance apart of the trees is a matter of choice. In Paris this is only 16 to 18 feet, but I think half a chain (33 feet) is quite close enough; it economises trees and gives plenty of room for the limbs of each tree to spread, and the intermediate lamp-posts, watering hydrants, or other standards are not crowded out. Each tree should have a cast-iron grating around its roots similar to the following drawing:-- [Illustration] This should be about 4 feet square. It prevents the ground getting hard about the trees, and permits air and water to enter to the roots. It also makes it easy to give any attention to the trees that they may require when young, such as manuring, digging, &c. The tree should also be protected with a slight iron grill or railing to prevent mischievous persons from cutting their names on the trunk, climbing up into the tree, or breaking off its branches whilst still young. The following sketch shows the description of grill necessary, which is light, cheap, and at the same time effective. [Illustration] The following interesting particulars of the manner in which street planting of trees is conducted in Paris will be useful, and are given _in extenso_:[221] “When the boulevarde is marked out and levelled, if the soil is of bad quality, as is nearly always the case, trenches are dug in the footway from one end of the boulevarde to the other. The width of this trench is usually about 6 feet, and its depth 4 or 5; and before filling it in drain-pipes are laid along the sides made with lapped joints so that the roots shall not enter between them. The trench is then filled with good garden earth, raising it a little higher than the level so as to allow for settling. In this ground the trees are planted about 6 yards apart. They should be carefully chosen with perfect roots, and moderately pruned. Formerly the stem was cut at about 9 feet from the ground, but this had the bad effect of preventing the top of the tree from being straight, and the practice has been given up. The trees are next staked and tied with wire over a neat wad of straw, which prevents all injury to the stem. A protecting cage, neither heavy nor very expensive, is placed round the tree to prevent accidents; and if the weather be at all dry at the time of planting, the trees are copiously watered.” The cost of planting a tree in the Paris boulevarde is thus given:[222] fr. c.