jr 



Mabch 20, 1913. 



The Florists^ Review 



n 



Hoose of Carnation The Herald at the Establishment of the Chicago Carnation Ca, Joliet, III. 



quent generation, wrinkled seeds pro- 

 duced all wrinkled, while twenty -five 

 per cent of the round gave all rounds 

 and the remaining fifty gave wrinkled 

 and round in the same proportion as 

 the F2 generation. From these data 

 Mendel formulated the following nu- 

 merical ratio for the F2 generation of 

 hybrids: 1:2:2, or twenty-five per cent 

 dominants, fifty per cent dominant re- 

 cessives and twenty-five per cent re- 

 cessives. 



Explanation of Terms Used. 



To facilitate further discussion along 

 this line, the algebraic expression 

 R+2RW-f E will be used to denote 

 the numerical value of the hybrids, R 

 denoting round, and W wrinkled, and 

 R W the hybrid between R and W. In 

 the hybrid R W the recessive W is 

 written in the lower case, thus R w. 

 Such an expression always denotes an 

 unexpressed or recessive character. For 

 the purpose of further discussion, it 

 seems desirable to introduce other 

 terms which are inimical to brevity and 

 to clear expression of thought. The 

 first term to be considered is that of 

 the gamete. This term is employed by 

 the biologist to denote the sexual cells 

 of a plant. It is supposed to contain 

 all of the heritable characters of a 

 plant or animal. The fusion of a male 

 and female gamete results in the for- 

 mation of what is technically known as 

 a zygote. If the fusing gametes are 

 of a similar constitution — that is, pos- 

 sessing identical unit characters, as in 

 the case of pure strains of plants — th( 

 resulting zygote is called a homozygote 

 because it possesses a homogeneous 



constitution. On the other hand, if 

 gametes of unlike constitution fuse With 

 each other the resulting union is called 

 a heterozygote, because it contains un- 

 like opposing characters. Therefore 

 each ovule and pollen grain developed 

 in plants produced from the R w seed 

 would theoretically contain the R and 

 W characters, and, according to the law 

 of chance, would combine in about 

 equal proportions. This may be best 

 illustrated in the following manner: 



Ovule 



Pollen 



Singles Crossed Witb Doubles. 



In group 2 we have an entirely dif- 

 ferent proposition. Here the female 

 seed parent possesses the S unit, and 

 the pollen or male parent the D or dou- 

 ble character. By combining these we 

 get the hybrid D s, as follows: 



Ovule 



Pollen 



S 





W --- 



Equals R -f 2 R w -f W, or the expression 

 of 1: 2: 1. 



It is important, however, to remem- 

 ber that Mendelian inheritance only 

 gives such an expression as the above 

 when the plants employed are gametic- 

 ally pure; that is, in which two oppos- 

 ing or contrasting characters do not 

 exist in the same gamete. With this 

 conception of Mendelian inheritance 

 and the factors which govern its ex- 

 pression, we may now redirect our at- 

 tention to the data previously sub- 

 mitted with reference to the results 

 secured from crosses in groups 1 to 4. 



In group 1 singles were crossed with 

 singles, and it will be remembered that 

 the resulting progeny were all single- 

 flowered. In this case it is evident that 

 the ovules and pollen grains of the sin- 

 gle flowering carnation only contain the 

 S unit character, and for that reason 

 it is only possible for the parent plants 

 to transmit the S unit to their progeny. 



Equals D s. S being recesslre, It Is unex- 

 pressed. 



Theoretically, then, the first genera- 

 tion hybrids all produce flowers of the 

 commercial type. The data presented 

 show that, while this was closely ap- 

 proximated, it was not absolutely at- 

 tained. Of the 1,004 seedlings which 

 were flowered, four produced single 

 flowers, 988 commercial, and twelve 

 were classed as doubles. In the light 

 of our present knowledge there is some 

 reason to doubt the accuracy of the 

 observation upon the twelve doubles 

 noted. It is quite possible that they 

 may have been rather fuU-petaled 

 bursters of the commercial type. How- 

 ever, be this as it may, the evidence 

 seems to overwhelmingly support the 

 idea that the single and double unit 

 characters of the carnations are sepa- 

 rate and distinct entities. The pres- 

 ence of a single plant in each of four 

 crosses may be accounted for by as- 

 suming that, through some accident in 

 making the cross or in emasculating the 

 flower, a pollen grain from a single 

 may have been transferred to the 

 stigma from the forceps used in per- 

 forming the operation. The percent- 



