THE EXPERIMENTAL MODIFICATION OF 



GERM-PLASM 



D. T. MACDOUGAL 



i 



The doctrine of an inviolable germ-plasm has formed the 

 foundation of many imposing edifices in biological thought, 

 and facilitated many advances in genetics and heredity during 

 the last two decades. The authors who have rigidly adhered 

 to the principles of the hypothesis and reasoned from its tenets 

 have exposed many fallacies which have been offered in ex- 

 planation of problems in evolution. 



This prevalence of theoretical considerations over mistaken 

 experiences has laid the foundation for an unreasoning devo- 

 tion to the idea of an independent germ-plasm, carrying agents 

 which may not be seen, measured, or tested in any practicable 

 manner, and which might consequently be termed "idealo- 

 plasm" with attributes approaching the supra-physical. 



The desperate straits of those who voluntarily consign them- 

 selves to the bondage of such a conception is well exemplified 

 by the group of writers who subscribe to the conclusion that all 

 evolutionary movement is due simply to recombination and re- 

 arrangement of qualities or factors already present in the 

 protoplasm. An additional illustration of the futile extremes 

 to which this view may be pushed is to be found in the recent 

 utterances of Bateson, who has arrived at the conclusion that 

 evolution is mainly and essentially loss of inhibitors, and re- 

 lease of activities previously latent or suppressed, an hypoth- 

 esis which predicates premutation. 



If it be allowed that the non-appearance of a character is a 

 direct loss of its determiner and that the appearance of a new 

 feature is the loss of a retarder or inhibitor which held it in 

 abeyance, then the answer to the question as to the method by 

 which organisms have arrived at their present condition is 

 obvious, but of a simplicity that is metaphysical instead of 

 actual and hence of little value, even tentatively, as a frame- 



Ann. Mo. Bot. Gard., Vol. 2, 1915 



(253) 



