TEE RED SUNFLOWER 375 



Branched habit X branched habit 



Small heads X small heads 



(2) CoRONATUsX Annuus (" Eussian ") 



Eed rays X yellow rays 



Dark disc X yellow disc 



Branched habit X unbranched habit 



Small heads X large heads. 



We later found a plant of lenticularis showing a little red on the rays, 

 and of course used this in a cross. 



Could we predict the result of these crosses? Yes, to some extent. 

 Could we regain the red as it was before the cross? Yes, no doubt, 

 but in order to explain how, it is necessary to digress. 



During the sixties, Gregor Mendel, Pralat at Briinn in Moravia, 

 experimented with plants, especially garden peas. He was the first to 

 appreciate the necessity of following up crosses for several successive 

 generations, tabulating the results in each case, and ascertaining the 

 numerical proportions of the differing forms resulting. He also took 

 pains to consider the different sets of characters separately, treating 

 them statistically as if they were different organisms. Working in this 

 way, Mendel discovered that when two varieties are crossed the result- 

 ing hybrid is frequently not intermediate, but resembles one or the 

 other parent. In other cases, when the hybrid, as a whole, seems inter- 

 mediate, the several characters are nevertheless found to correspond 

 with those of one or the other parent.' When this sort of thing occurs, 

 the character which comes uppermost in the cross is said to be domi- 

 nant, the one which remains latent or hidden is called recessive.^ Inas- 

 much as fertilization results from the fusion of the germ-cells of the 

 two parents, it is evident that each individual hybrid must contain ma- 

 terial derived from both, although only the characters of one parent 

 may be visible. Now Mendel found that when hybrids obtained as 

 described were crossed together in the next generation he got, in simple 

 cases, three of the " dominant " type to one of the " recessive." Of 

 course the proportions would not be always thus, but whenever the 

 number of cases was large they approximated so closely to the three-to- 

 one ratio, that he became convinced that this was no accident. A 

 simple theory was formulated, according to which the results arose 

 from the chance combination of the elements in the germ cells. We 

 may now make this clearer by a diagram in which D stands for the 

 character which is dominant, E for that which is recessive. 



First cross, DD X ER 



* The matter is complicated by the fact that the ' ' recessive ' ' condition may 

 result from the simple absence of the dominant factor; or one factor, when 

 present, may inhibit or else hide a second. For the latter class of cases the 

 terms epistatic and hypostatic have been proposed by Bateson. 



