14 HORTICULTURAL SOCIETY OF NEW YORK. 



(3) Differential Characters. 



The third point worthy of note in the methods of Mendel is that the 

 characters selected for crossing must not only be single and constant, but also 

 differential in the two parents. If the single characters be nearly alike in the 

 two parents it will be impossible to determine which parent the offspring re- 

 sembles in that character, because all three would necessarily be nearly alike, 

 i. e., the offspring and its two parents. On the other hand, the wider the 

 difference between the pair of parental characters, the more clearly defined will 

 be the single character in the resulting offspring, and consequently the easier 

 it will be to refer the resemblance in the offspring to either parent. 



Mendel, in his experiments, takes single constant characters in the parents 

 which are distinctly differential and which can be clearly defined in the 

 offspring. 



(4) Dominant Characters. 



The fourth point in Mendel's methods is distinctly new, and that is the 

 crossing together only of Dominant and Recessive characters, i. e., one of the 

 characters of the differential paris is always distinctly dominant over the other 

 one, which latter is known as the Recessive character. 



This serves a useful purpose in giving uniformity in the first generation, 

 and thus avoids the great difficulty of working on to the next generation with 

 results which are not uniform. 



For instance, if the pair of characters were of fairly equal potency, they 

 would, on the whole, be intermediate either blended or mosaic, tending to one 

 parent and the other alternately. It is obvious, therefore, that in a case like 

 this, if one wished to carry on the experiment to further generations, the lack 

 of uniformity in the first generation would complicate the experiment so much 

 as to make it almost unworkable. 



Mendel avoids this by the selection of Dominant and Recessive characters 

 only, consequently his results can easily be recorded and tabulated statistically 

 in all the generations. 



(5) Large Numbers. 



The fifth point of note in Mendel's methods is his use of large numbers, 

 and in -this respect he was without doubt far in advance of his predecessors 

 and contemporaries. In the older experiments, for the most part, only a few 

 individuals of each cross were raised, and hence the range of variations appar- 

 ent was either extreme or scarcely perceptible, according to chance and cir- 

 cumstances. 



This no doubt accounts in some measure for the many contradictory results 

 obtained by different experimenters at different times. Mendel avoided these 

 difficulties by raising large numbers of individuals in each generation, and in 

 that way practically gauged the total range of variation in each case.e 

 (6) Many Generations. 



Now we come to the sixth and last method of Mendel to be noted here, 

 and that is that he was not content to stop at the first generation or even 

 the second, as so many of his predecessors were, but he in all cases carried on 

 the experiments to the third and fourth generations and in some cases to the 

 fifth and sixth generations. Mendel saw clearly that this was absolutely neces- 

 sary, though at the same time the work must have been very laborious, and it 



