Page:Popular Science Monthly Volume 69.djvu/218

no evidence exists to show that the farm, garden or nursery has ever produced alterations which were strictly and continuously inheritable, or were present, except under environic conditions similar to those by which the alterations were induced, although vague statements and erroneous generalizations to the contrary are current. It it true of course that structural and physiological changes may be induced in a strain of plants in any generation, which may persist in a share to the second, or even in some degree to a third, but no longer.

So far nothing has been offered which would tend to disprove these conclusions.

It is by no means intended to maintain that the stream of heredity may not be altered by the action of external agents, and the possibility of having such changes ensue in experimental cultures beckons with alluring finger to the observer. So important do I hold this aspect of the matter, that a series of experiments, yet in progress, were begun previous to the mutation cultures, and these tests have been continued and expanded until one plant is now undergoing culture in New York, Jamaica, and in connection with the Desert Laboratory, at sea-level and altitudes of 2,300. 5.000. 6,000 and 8,000 feet, and under conditions widely different from those prevalent in its original habitat. If at the end of the decade, this, or any other of the species under test, shows any transmission of the characters induced by the various localities, the care and work necessary in the experiments will be richly rewarded. In this comment reference is had to factors presented by tillage, or entering into the environment of plants in their native habitats.

Announcement has been previously made that mutations, breaks, saltations or discontinuous action may be caused in inheritance by forces external to the protoplasts and cells, which are the true bearers of the hereditary characters (see p. 17).

The technique of the methods by which such changes are induced might be simulated by the action of gaseous emanations, from the soil. radio-action, foreign pollen, or by the stings and incisions of insects, but certainly these possible factors would lie as potent with wild as with cultivated plants, as may be seen in the description of the manner in which such changes have been produced.

 

The Method of Pedigree-cultures

The importance of pedigree-cultures of plants as a means of tracing the course and action of heredity has been notably emphasized by recent investigations, and it will be profitable to go into a detailed statement of the manner in which experiments of this kind are carried out. One of the most striking developments of methods of research in botany has been the continually increasing extent to which taxonomists are having recourse to observations upon growing material in botanical gardens and experimental grounds. In the determination of