EFFECT OF SOLUTIONS ON GERM-PLASM

The idea that solutions of various kinds might be introduced into the plant, and that modifications of the ontogenetic procedure might be thus brought about, has been in the minds of many workers in the laboratory. Developing inflorescences have been excised and set in vessels containing salt solutions, and in other cases substances were applied to cut surfaces of the vegėtative parts of the reproductive organs without result.

This in part was suggested to Darwin by vegetable galls, and in the first chapter of the Origin of Species (page 7) we find him saying:

"Such facts as the complex and extraordinary outgrowths which invariably follow from the insertion of a minute drop of poison by a gall-producing insect, show us what singular modification might result in the case of plants from a chemical change in the nature of the sap."

That his interest in this matter was continued is evidenced by the following from Life and Letters:

"Shortly before his death, my father began to experimentise on the possibility of producing galls artificially. A letter to Sir J. D. Hooker (November 3, 1880) shows the interest he felt in the question:

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"I was delighted with Paget's Essay.' I hear

'Disease in Plants, by Sir James Paget. Gardeners' Chronicle, 1880.

that he has occasionally attended to this subject from his youth. I am very glad he has called attention to galls: this has always seemed to me a profoundly interesting subject; and if I had been younger would take it up.'

"His interest in this subject was connected with his ever-present wish to learn something of the causes of variation. He imagined to himself wonderful galls caused to appear on the ovaries of plants, and by these means he thought it possible that the seed might be influenced, and thus new varieties arise. He made a considerable number of experiments by injecting various reagents into the tissues of leaves, and with some slight indications of success.

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In response to a request for a more detailed account of work that may have been done on this subject by the elder Darwin, Professor Francis Darwin writes under date of November 27, 1908:

"I am sorry that I can give you no further information about the experiments on galls. My recollection is that we tried only injections with leaves and stems, and that no actual experiments were made on ovaries. I have never looked at his notes and do not know where they are at this moment, but I feel pretty sure that no definite results were obtained. I think acetic or formic acid was used in the experiments."

In the course of my extensive cultures dealing with mutations, the theoretical conclusions of De Vries as to the pre-mutation period came up for serious consideration, and in order to obtain some evidence upon this point, as well as to test the assumption that the actual changes upon

1 Life and Letters of Charles Darwin, by F. Darwin, II, p. 517, 1905. New York.

which mutation rests ensue previous to the reduction divisions leading to the formation of the reproductive nuclei, some new methods of experimentation were developed. Among other operations, solutions of sugar, calcium, potassium, and zinc were injected by the use of hypodermic syringes into the developing ovaries of Raimannia, one of the evening primroses, early in 1905, with the result that out of the several hundreds of seeds borne by the treated ovaries sixteen individuals were found to be notably atypic, among other characters lacking the trichomes which are so conspicuous with the parental form. These reproduced themselves in the second and third generations, coming true to the newly assumed characters.

The same method was tried with Oenothera biennis (Plate II), the common evening primrose of waste lands in eastern United States, with the result that two individuals were found among the seedlings which were different from the parents in a series of characters so distributed through the ontogenetic period that the derivatives could be recognized by the first two leaves, while the cotyledons were still waxing. This form is now being cultivated at the Desert Laboratory in the fifth generation, and is being thrown against the climatic selective factors in the mountain plantations at various altitudes.

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1 The derivatives, lettered D in Plate II, are to be compared with the typical young plants, lettered T.