IRISH GARDENING 



67 



Mendelism. 



fourth paper. 

 By Professor James Wilson, M.A. 

 Last month tAvo diagrams were not printed as 

 tho\ Avere intended to have been, and the 

 ilhnnination they were expected to give to two 

 very difficuh points was lost. Before proceeding 

 farther it will be well to have those two diagrams 

 properly displayed. The first was to illustrate 

 how the materials for roundness and wrinkled - 

 ness are distributed in the hybrids, and should 

 have been as follows : — 



IN THE POLLEN : 



R 



w 



IN THE OVARIES 



R 



W 



The next was to illustrate the sixteen possible 

 combinations produced by the hybrids of 

 parents M'hich differed in tMo jiairs of characters, 

 and should have been as follows : — 



gg 



gg 



We may noAV sum up the chief results Avhich 

 can be gathered immediately from Mendel's 

 experiments. They are : — 



(a) The progeny of hybrids are of different 

 kinds, and the number of kinds depends upon 

 the niunber of characters in Avhich their parents 

 differed. If the parents differ in (me pair of 

 character, the hybrids have tAVo kinds of 

 progeny ; if the j)arents differ in tAvo pairs, 

 the hybrids have four kinds ; and so on : the 

 number of kinds of progeny being doul)led 

 for every additional pair of characters in A\liich 

 the original parents differed. 



(h) The numbers in each kind produced by 

 the hyl)rids increase in nuithematical order, 

 according as the pairs in which the original 

 parents differed increase, thus : — 



For one pair ',i : I 



For two pairs i> : 3 : 3 : 1 



For three pairs 27 : !) : U : i) : 3 : 3 ; 3 : 1 

 and so on. 



(c) In each kind produced 1)>- the hybrids a 



certain proportion of individuals breeds true. 

 In the smallest group every individual breeds 

 true ; in e\'erv group of 3, one indiAudual breeds 

 true ; in every group of 9, one individual breeds 

 true, and so on. 



(d) The different characters borne by the 

 hybrids" progeny — that is, of the kinds they 

 produce — which liaAe been the subject of 

 obserA^ation may lie represented generally as 

 foUoAvs : — 



When there are tA\-o kinds — 



X 



3 



Where there are four kinds- 

 X 



X 



Y 



9 



X X 



A- Y y 

 3 : 3 : 1 



Where there are eight kinds- 



X 



X 

 Y' 

 Z 



•>7 



X 

 Y 



z 



9 



X 



V 



Z 



9 



X 



Y 

 Z 



9 



and so on. 



From these results the 

 deductions can be made : — 



folloA\ing simple 



(1) As to the number oj new kinds or 

 varieties j^roduced. — Since there are ahvays 

 only tAVo original parents and both their tyi)es 

 are found among the hybrids" progeny, the 

 number of ncAv kinds produced must be the 

 total number of kinds jiroduced by the h\brids 

 minus tAVo, thus : — 



Total Number 

 of kinds in the 

 Hybrid'.s Progeny 



2 



4 



8 

 10 

 32 



Number of 

 kinds in tiie 

 Original I'arent.- 

 o 



2 

 2 



New kinds 

 U 



2 



G 

 14 

 30 



and so on. Thus, if a gardener A\-ishes to produce 

 a ncAv A'ariety, he must begin by mating parents 

 Avhich differ in more than one pair of characters ; 

 and, the more the characters in Avhich the 

 original parents differ, the more hcav kinds Avill 

 he produce. 



(2) As to the jKirents to he mated. — It is not 

 necessary that one parent should carry all the 

 dominants and the other all the recessives. 

 If A\-e look back to paiagra])]! [d) at the set of 

 progeny containing four groiqis Ave shall see that 

 it does not matter A\hether jiarents carrying the 

 characters XY be mated Avith tho.se carrying 

 xy or Avhethcr parents carrying Xy be mated 

 Avith those carrving xY. In each case the same 



