170 EVOLUTION AND GENETICS 



therefore, until further and more critical evidence is 

 obtained as to the nature of the effect, if any, that 

 was induced in Guyer's experiment. 



The next best case is that of Griffith and Detlef- 

 sen. Rats were rotated for several months in cages. 

 Some of the young born outside the cage showed 

 irregularities in their gait, and when tested gave a 

 different and specific response according to whether 

 their parents had been rotated to the right or to the 

 left. Detlefsen states that the disequilibrated rats 

 showed frequent pathological sequelae, such as dis- 

 charges from the ears; and this, he says, raises the 

 question "whether Griffith has not merely presented 

 us with numerous specimens of some vertebral dis- 

 ease." The disease once begun might be contagious, 

 but he adds, "It is difficult to compromise this hy- 

 pothesis with Griffith's contention of specificity." 



This brings us finally to a point where something 

 more definite may be said and therefore said briefly. 

 Blakeslee and Belling have shown that if, during the 

 maturing of the reproductive cells of a flowering 

 plant, the common jimson weed, the jDlant is sub- 

 jected to cold, the germ-cells may be so affected that 

 the distribution of the chromosomes is on rare oc- 

 casions altered, and a jDlant may be produced that 

 has double the normal number of chromosomes. 

 This change carries in its wake some corresponding 

 changes of character. Changes of both these kinds 

 often take place when the egg is not treated, and 



