of this description, covering a row
of trees, may be filled with fumes from a position at the end of the
row, where a generating plant on a trolley may be situated. At the
opposite end another trolley is stationed, and each movable vehicle
carries an upright mast or trestle for the support of the strong cable
which passes along the row over the tops of the trees and is stretched
taut by suitable contrivances. Attached to this cable is a flexible
tube containing a number of apertures and connected at the generating
station with the small furnace or fumigating box from which the
poisonous gases emanate.

Along the ground at each side of the row are stretched two thinner
wires or cables which hold the long tent securely in position. The
method of shifting from one row to another is very simple. Both
trolleys are moved into their new positions at the two ends of a fresh
row, the fastenings of the tent at the ground on the further side
having been released, so that the flap of the tent on that side is
dragged over the tops of the trees and may then be drawn over the top
cable and down upon the other side. Seen from the end, the movements
of the tent thus resemble those of a double-hinged trestle in the form
of an inverted V which advances by having one leg flung over the
other. For this arrangement of a fumigating tent it is best that the
top cable should consist of a double wire, the fabric of the tent
itself being gripped between the two wires, and a flexible tube being
attached to each.

As progress is made from one row to another through the drawing of one
flap over the other, it is obvious that the tent turns inside out at
each step, and if only one cable and one tube were used, it would be
difficult to avoid permitting the gas to escape into the outer air at
one stage or another. But when the tubes are duplicated in the manner
described, there is always one which is actually within the tent no
matter what position the latter may be in. It is then only necessary
that the connection with the generating apparatus at the end of the
row should be made after each movement with the tube which is inside
the tent. For very long rows of trees the top cable needs to be
supported by intermediate trestles besides the uprights at the ends.

The gas and air-proof tent can be used for various other purposes
besides those of killing pests on fruit trees. One of the regular
tasks of the tree-doctor will be connected with the artifici