During the past few years a tremendous quantity of publicity has been given to the use of various substances to stimulate growth in plants. Most of the emphasis has been laid on the use of such substances for the rooting of cuttings of woody plants such as Camellia, rhododendrons, holly and others which ordinarily are extremely difficult to root, and for accelerating the rooting of other cuttings which are more easily rooted with the customary propagating practices. More recently, the effect of these same substances on seed germination has been capitalized upon in the seed trade. As is frequently the case in commercial propaganda, promises are made which far exceed, and in some cases have but little bearing on, the actual facts which have been demonstrated in wellcontrolled scientific experiments. For this reason, as well as because of the confusion and disagreement which appears to exist among the various investigators themselves, it has seemed wise to make an effort at this time to give our readers some notion of the actual principles involved in the use of growth substances, and of what they can and cannot be expected to accomplish.