The Relation Between Age of Stem Tissue and the Capacity to Form Roots

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Abstract
Although there is considerable variation among closely related species and varieties of plants, it is evident that there is a relation between the age of plant tissue and its natural capacity to form adventitious roots. This age factor can generally be overcome with the aid of hormone-like substances which serve as chemical growth regulators, and which have the power to induce adventitious roots on tissues where roots do not naturally appear. Cuttings of the lilac taken in May have the capacity to grow adventitious roots. This capacity gradually declines until it is completely gone by July. Cuttings of apples taken early in May form roots when treated with growth substances, but gradually decline until June. Cuttings from seedlings of difficultly propagated species have the capacity to form roots, whereas cuttings from old trees of the same species can seldom be induced to root, even with the aid of hormone-like substances, because they no longer have the capacity to make use of them. The mechanism in plants through which chemicals act is not understood, and it is further complicated because closely related species differ widely in their response. The new use of plant hormones has thrown some light on the subject, but it is reasonably certain that the change in structure or protoplasm with age is a major controlling factor.

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