Section 100. Except where the Companies agree that the reference shall be made to a single arbitrator, the reference shall be made as follows, to wit:

100. Except where the Companies agree that the reference shall be made to a single arbitrator, the reference shall be made as follows, to wit:— - where there are two Companies, the reference shall be made to two arbitrators; - where there are three or more Companies, the reference shall be made to so many arbitrators as there are Companies.