Modification of Germinal Constitution of Organisms 205 



through three or four generations in properly guarded 

 cultures. 



MacDougal has attacked this problem from a strictly 

 experimental standpoint in the effort to discover a cause, 

 and to arrive at an understanding, of the phenomena of 

 "mutation" as described by DeVries in Oenothera. The 

 method which he has used is to inject solutions of various 

 kinds into the ovaries immediately before fertilization. 

 Later, Gager, by subjecting seeds to the action of radium 

 bromide, has shown that in plants physical factors incident 

 upon the germinal materials can and do produce germinal 

 changes that are permanent and persist in undiminished 

 vigor in subsequent generations. 



MacDougal's experiments, wherein zinc salts, cane 

 sugar, etc., were injected into the ovules of plants, show 

 that permanent changes resulted. JNIacDougal's method 

 and the reasons therefor are as follows: 



Having carried on pedigree cultures with a large number of species 

 for several years and having encountered some which did and others 

 which did not give rise to aberrant indi\'iduals, attention was directed 

 to the possibility of inducing changes in the hereditary elements in 

 such a manner that the qualities transmitted would be altered or 

 destroyed. A theoretical consideration of the subject seemed to 

 indicate that the changes constituting the essential operation of muta- 

 tion ensued in a stage previous to the reduction divisions in the embryo 

 sac, or the pollen mother cells. It was planned therefore to subject 

 these structures to the action of chemical agents, not ordinarily encoun- 

 tered by the elements in question, at a time before fertilization occurred. 

 The tests were planned to include the use of a solution of high osmotic 

 value, and mineral compounds, some of which are to.xic in concentrated 

 solutions and stimulating in the proportions used. The probability 

 of success would be heightened with the number of ovules contained 

 in any ovary operated upon, and therefore the conmion evening 

 primrose, Oenothera biennis, Raimannia odorata, a relative of it, and a 



