4io 



The Living Plant 



FIG. 172. A diagram to illustrate the three leading 

 explanations of the method of evolution. 



A spherical organism, represented by the circles, is 

 assumed to be living under conditions where in- 

 crease of size is advantageous. The course of 

 evolution is condensed to eleven generations, be- 

 ginning on the left and running up to the right. 

 The dotted lines show the connection between 

 parents and offspring, and the shading in- 

 dicates extermination of the less fit. 



The upper figure represents the operation of 

 natural selection. Two offspring are as- ,/_ 

 sumed in each generation of which 

 one varies to a size larger than 

 the parent, the other remaining 

 the same. 



The second figure represents 

 the operation of transmis- 

 sion of acquired char- 

 acters. As all the 

 offspring are alike 

 from this 

 point of 

 view, only 

 one of each 

 generation 





is shown. The 

 adult individuals 

 are assumed to ac- 

 quire a larger size 

 under stimulation, 

 and to transmit 

 that larger size to 

 their offspring. 

 The lower figure rep- 

 resents the operation of mutation. The indi- 

 viduals are substantially alike for a number 

 of generations, then suddenly give origin to 

 a larger type, which persists unchanged for 

 a time, only to give origin to a still larger, and 



cause of their adaptations to their surroundings. It will be evident 

 to the reader that the principle, while logically strong, is highly 



