102 



HEREDITY AND EVOLUTION IN PLANTS 



characters of the parent plant were carefully noted and 

 recorded by photographs and written descriptions, and by 

 preserving dried and pressed herbarium specimens. The 

 plants of the second generation were carefully guarded 

 from being cross-pollinated, and thus "pure" seed were 

 secured for a third generation. This was continued often 

 for 25 or 30 generations of the plant, requiring as many 



FIG. 49. Hugo de Vries. His pioneer studies of osmosis resulted in 

 fundamental contributions to our knowledge of that subject; his mutation- 

 theory is one of the most important contributions to the study of evolu- 

 tion since Darwin. 



years when a species produced only one crop of seed a 

 year. Very careful records and preserved specimens were 

 kept of the plants of each generation, and accurate com- 

 parisons were made to see if any individuals showed a 

 tendency to vary widely from their parents in any sig- 

 nificant way, such as showing entirely new characters, not 

 expressed in the parents, or failing to manifest one or more 

 of the characters of the parent. 



