90 



The Journal of Heredity 



MORE VIGOROUS HYBRIDS WITH LESS VIGOROUS INBRED WILD PLANTS 

 Crepis capillaris is a wild plant of the sunflower family. It is a native of the Mediterranean 

 countries, and is growing wild in North and South America. Plants grown from seeds which were 

 collected in two widely separated parts of California have shown interesting effects of cross- 

 breeding and inbreeding. The hybrid plants (in the centre row) between inbred plants of the 

 same age show pronounced hybrid vigor and development. (Fig. 31.) 



were present in either of the parents. 

 The Hnkage of such dominant genes 

 to recessive genes or to dominant genes 

 that influence size or vigor adversely 

 reduces the possibility of securing such 

 dominant races in a homozygous con- 

 dition. For this reason the vigor 

 noticed in the Fi generation is less 

 marked in the Fa and subsequent 

 generations where segregation and re- 

 combination of the genes of the h\ are 

 made e\ident. Most of our knowledge 

 regarding inbreeding and crossing of 

 inbred strains has been derived from 

 experiments on maize, a plant which 

 has been subject to artificial selection 

 for centuries since its domestication. 

 The question has arisen whether a 

 cross-fertilized species which had never 

 been domesticated and thus subjected 

 only to natural selection would exhil)it 

 inbreeding and cross-breeding results 

 similar to that described above. The 

 answer to such a question will require 

 controlled experimentation upf)n a 

 number of species, but a beginning 

 has been made with Crepis rapillaris, 

 a wild cross-fertilized plant belonging 

 to the sunflower fann'b-. 



INBREEDING REDUCES VIGOR AND SIZE 

 IN CREPIS 



Crepis capillaris is a native of the old 

 world, found particularly in the coun- 

 tries about the Mediterranean and 

 spreading out over Europe, Asia, 

 Africa and adjacent islands. It has 

 been introduced and is growing wild in 

 both North and South America. The 

 flowers are perfect, and both cross 

 and self-fertilization takes place. No 

 records haAc been found where this 

 plant has been subjected to extensive 

 selection or domestication inasmuch as 

 it has no properties of economic Aalue. 



Seed collected from wild plants 

 growing in two locations about 300 

 miles apart in California were used in 

 the experiments of inijreeding. At 

 the beginning of the experiment the 

 I)lants were very similar in most 

 characters and in size. The practice of 

 inbreeding was started to purify the 

 material which obviously was heterozy- 

 gous. In the second generation of 

 inbreeding there was some evidence of 

 reduction in \igor and size, but the 

 results of the .Srd and 4th generations 

 k'ft no c|uesli<)n as to what was taking 



