1915] 



MACDOUGAL — MODIFICATION OF GERM-PLASM 273 



ready determined. This limitation of the possibilities of 

 morphogenesis is the chief one in any expectancy of duplica- 

 tion of results in successive treatments, outwardly mechanic- 

 ally identical. 



The variables in any experimental setting are many, and 

 the briefest consideration of the physical effects consequent 

 upon the introduction of a foreign solution to the vicinity of 

 the embryo-sac, reveals at once the lack of probability of exact 

 repetitions in a mechanism so complex. The conditions are 

 much different from those which would be presented if free 

 floating eggs or sperms were immersed in a solution. If we are 

 able to induce other changes in Scrophularia besides those 

 shown, they will be quite as important in demonstration of the 

 fact that germ-plasm had been modified as if they were exact 

 repetitions of previous inductions. If previous results were 

 exactly recalled there might be some suggestion of premuta- 

 tion. 



It is evident that the experimenter who wishes to proceed 

 with the greatest precision and least loss of effort will first 

 test the genetic strictness of his living material, ascertain the 

 rate and manner and diffusion of solutions in the ovary and 

 ovules, the time of pollination and the rate of development of 

 the tube in reaching the egg. Next, the structure and number 

 of ovaries and the traumatic reactions of the entire pistil are 

 to be taken into account. Having also traced out the simpler 

 features of pollination and fertilization, the operator should 

 test the effects of various reagents which may neutralize pro- 

 teins, including enzymes, or act as excitators or catalyzers. 

 Without enlarging too much upon the difficulties to be encount- 

 ered in the experiments described in this jmper, they may be 

 illustrated by the fact that over fifty operations upon Scrophu- 

 laria in July, August and September, 1914, at Carmel, Cali- 

 fornia, were total failures, as the ovaries perished before 

 reaching maturity. 



Finally, many present interests in phylogeny and genetics 

 will be concerned with the nature of the evolutionary move- 

 ment which is simulated by the alterations which have been 

 induced experimentally by the method described. Some of 



