9^ 



The Journal of Heredity 



A FIRST GENERATION HYBRID COMPARED TO AN INBRED PLANT 



The greater vigor of the hybrid at the left is evident in this comparison with the inbred plant 

 which shows slower development and total size. Both hybrid and inbred plants were grown in 

 both four and six inch pots but the increased root space and quantity of soil did not alter the 

 relation of vigor in the plants. (Fig. 34.) 



place. These plants were smaller and 

 murh slower in growth than non-inbred 

 phinls. Inbreeding in this wild plant 

 which is in nature largely cross fer- 

 tilized does cause marked retluction of 

 vigf)r and rate of development. Thus 

 both they and maize behave in a similar 

 way when subjected to inbreeding. 



W'hen inbred non-related strains of 

 corn are crossed the prf)geny show a 

 return to the size and vigor of the par- 

 ents before inbreeding was practice<l. 

 In order to compare the wild plant 

 Crepis with the domesticated i)lant 

 maize in this respect, the inbred strains 

 of Crepis were crossed together and 

 to non-inbred strains. The results 

 (Figs. .SI to 34) of these crosses again 

 confirmed the similarity of the l)eha\ior 

 of inbred maize and inbred CVe|)is. 



The plants inider domestication are 

 not subjected to the same se\ere 

 natural selection agencies common to 

 wild i)lants. It is therefore j^ossible for 

 characters to exist in cultivated plants 

 which would not be able to persist in a 

 wild state. One would expect that 

 the germplasm of wild species wouUl be 

 to a considerable extent i)iirifie<l of the 

 genes which cause the production of 



harmful and abnormal characters by 

 the elimination of most of the weak 

 forins through natural selection. These 

 experiments with Crepis however show 

 that the germinal material is far from 

 being in a state of purity or a state of 

 homozygosity. If it had been nearly 

 homozygous little reduction would have 

 resulted when continued inbreeding 

 was practiced and we would have had a 

 condition similar to that in barley, 

 wheat and peas where inbreeding (the 

 nonnal method of reproduction) does 

 not cause a reduction in general vigor or 

 in rate of growth. 



FOUR GENERATIONS 



In Figure 31, cultures 113 and 114 

 are plants that have been subjected to 

 inbreeding for four generations. The 

 plants marked 115 are Fi hybrids 

 I)rodu<ed 1)\' crossing the inbred strain 

 to a non-inl)red and non-related strain. 

 All plants were grown in four inch 

 clay pots and were arranged, during 

 their growth periinl, with h>brid plants 

 between inbred plants asin Figure 31. 



Inbreil and Inbrid plants were also 

 grown in six inch pots but as shown in 

 Figure 34, the increased root space 



