ModiJicatio)i oj Germinal Conslitulion of (>ri^a)iisms 205 



through three or four generations hi properly guarded 

 cukures. 



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 Oaiotlicra. The 

 method which he has used is to inject solutions of various 

 kinds into the o\'aries immediately before fertilization. 

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

 bromide, has shown that in plants ph>'sical 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. MacDougal's method 

 and the reasons therefor are as follows; 



Having carried on pedigree cultures with a large numlDe ■ of species 

 for several vears and having encountered some which did and others 

 which did not give rise to aberrant individuals, 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 suljject seemed to 

 indicate that the changes constituting the essential operation of muta- 

 tion ensued in a stage previous to the reduction divisions in the eml)r\'o 

 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 (jccurred. 

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

 \-alue, 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 common eveiiuig 

 primrose, Ociiollicra biennis, Riiimannia odorala, a relative of it, and a 



