1923] FULLER, THE ROSE FAMILY 147 



or in other words, the mechanism for heredity. There was accumu- 

 lated an abundance of evidence for the theory that most of the in- 

 herited characteristics are carried by chromosomes, small bodies in 

 the nuclei of cells. However, these students of the cells (cytologists) 

 did not pay much attention to living plants and animals. 



The first important work pertaining to heredity from the experi- 

 mental field, was done by an Austrian Monk, Gregor Mendel, in the 

 middle of the last century. In the garden of the monastery, he grew, 

 experimented and observed plants. Mendel's epoch-making experi- 

 ments were mostly confined to the common garden pea. He crossed 

 a rough-coated seed variety with a smooth-coated variety and all of 

 the offspring produced smooth-coated seeds. In the second generation 

 the two contrasting characteristics separated. Seventy-five percent 

 of the seeds were smooth-coated and twenty-five percent were rough- 

 coated. The rough-coated seeds always bred true. Some of the 

 smooth seeds bred true while others gave rise to smooth and rough- 

 coated seeds in the proportion of three smooth to one rough. He 

 tried a number of other contrasting characteristics and found that 

 they worked out the same way. 



Mendel published the results of his work in 1865 but the paper re- 

 mained almost unknown until about 1900, when it was discovered 

 simultaneously by three scientists and created a sensation in the scien- 

 tific world. Later, workers produced various kinds of hybrids ex- 

 hibiting characteristics intermediate between the parents. Many 

 scientists believed that hybridization is one means by which a species 

 gives rise to new forms. In a large number of cases hybridization is 

 responsible for variation. 



Another theory relative to origin of species was advanced by Hugo 

 de Vries of Holland. De Vries had transplanted a number of evening 

 primroses (Oenothera) to an experimental garden. Some of the off- 

 spring varied greatly from the parent plant. DeVries' theory was 

 that species rose by a sharp differentiation from the parent plant. 

 The Mutation theory, as it was called, remained unchallenged for a 

 time. About 1914, E. C. Jeffry'^*' pointed out that the evening prim- 

 rose plant used by DeVries probably was a hybrid and if it was, the 

 variability of the offspring would be explained. In a large number of 

 cases of variation, hybridization is responsible but there are a few 

 cases which hybridization does not explain and DeVries' Mutation 

 theory does. Other causes for variation are— geographical isolation, 



'^oE. C. Jeffry, "Spore Condition in Hybrids and the Mutation Theory of DeVries" — Botanical 

 Gazette, voL 58, p. 322. 



