228 PROBLEMS OF GENETICS 



no rosette, growing to a much smaller size than the parent, and 

 was totally glabrous instead of being very hairy as the parental 

 type is. I was shown specimens of these plants by the kindness 

 of Dr. Britton in the Bronx Park Botanic Garden in 1907 and 

 can testify to their very remarkable peculiarities. They had a 

 somewhat weakly look, and might at first sight be thought to be 

 a pathological product, but they had bred true for several 

 generations. From the evidence, however, I am by no means 

 satisfied that their original appearance was a consequence of 

 the treatment applied. This treatment was of a most miscel- 

 laneous description. Two of the mutants came from an ovary 

 which had been treated with a ten per cent, sugar solution. Ten 

 came from one into which a 0.1 per cent, solution of calcium 

 nitrate had been injected. One was from a capsule which "had 

 been exposed to the action of a radium pencil." MacDougal 

 speaks of these results as decisive, but clearly before such evidence 

 can be admitted even for consideration it must be shown by con- 

 trol experiments that the individual plants which threw the 

 mutant were themselves breeding true in ordinary circumstances. 

 Nothing is more likely than that the mutant was an ordinary 

 recessive. I may add that Mr. R. H. Compton made a number 

 of experiments with Raimannia odorata, raised from seeds kindly 

 given me by Dr. Britton, injecting the ovaries with a variety of 

 substances, including those named by MacDougal; but though a 

 numerous progeny was raised from the ovaries treated, all were 

 inormal. MacDougal relates also that some mutational forms 

 came from ovaries of Oenothera Lamar ckiana exposed to radium 

 pencils, and also from Oenothera biennis injected with zinc sul- 

 phate a peculiar mutant was raised, but taking into account the 

 frequency of these occurrences in those species, he very properly 

 regarded this evidence as of doubtful application. In a later 

 paper, 16 however, he has returned to the subject and affirms his 

 conviction that the appearance of a mutant among seedlings 

 raised from an ovary of Oenothera biennis treated with zinc 

 sulphate was really a consequence of the injection, saying that 



16 MacDougal, D. T., "Alterations in Heredity induced by Ovarial Treat- 

 ments," Bot. Gaz., vol. 51, 191 1, p. 241. 



