M 



I^ISH GARDENING 



But this leads to the crucial observation. 

 Both these kinds of true breeding seeds are the 

 progeny of the hybrids. Thus, Avhen their 

 parents differ in one pair of characters, the 

 hybrids produce two kitids of jirogenj), each of 

 ivhich contains equal numbers of individuals 

 tvhich breed true. 



The same observation can be made with 

 regard to Mendel's exjieriments when the original 

 parents differed in two pairs of characters. 

 The original parents were round with yellow 

 albumen, on the one hand, and wrinkled 

 with green albumen on the other. The hybrids 

 were all round with yellow albunien ; but they 

 produced four kinds of progeny, and when these 

 were bred into another generation, each kind 

 was found to contain equal numbers which bred 

 true. The full statement is as follows : — 



Original ) Round with yellow albumen and wiinkleil 

 Parents \ with green albumen. 



A similar result was found when the original 

 parents differed in three pairs of characters. 

 Eight groups were produced numerically in the 

 ratio 27:9:9:9:3:3:3:1. The original parents 

 were round, with yellow albumen and coloured 

 seed coat, on the one hand, and wrinkled, with 

 green albumen and white seed coat, on the other. 

 It will save space in displaying the full statement 

 if we write the initial letters of the characters 

 for the characters themselves. Thus R = round, 

 w = wrinkled ; Y = yellow ; g = green ; C = 

 coloured, and wh ^ Avhite. 



Original 

 Parents 



RYC and wgc. 



Thus in these tAvo cases, in whicli the original 

 parents differed in two and three pairs of 

 characters, we have the hyl)rids producing four 

 types in the first case and eight in the second, 

 and in both cases equal numbers of true breeding 

 individuals were found of every tyj^e. 



The main I'esults of Mendels experiments 

 may noAv be summed up thus : — 



(1) The number of types or kinds the hyl)rids 

 produce are doubled with every additional pair 

 of characters in which their parents differ, 

 thus :— 



Differing pairs of characters : 1, 2, 3, 4, 5. . . 

 Number of types produced : 2, 4, 8, 16, 32 . . . 



(2) The numbers in each ty]:!e increase in 

 mathematical ratio, as the differing pairs of 

 characters increase, thus : — 



In one pair 

 For two pairs 

 For three pairs 



27 : 9 : 9 



. 3 

 . 9:3:3 

 9:3:3:3 



and so on. 



(3) Among every type produced by any one 

 set of hybrids, equal numbers of pure breeding 

 individuals are found. 



The next part of Mendel's work was to formu- 

 late a theory which should explain these pheno 

 mena. We shall put his argument in abbre- 

 viated and slightly different form. Mendel laid 

 more stress on some other observations which 

 have not been mentioned here, as it requires more 

 than an ordinary amount of mathematics to 

 follow them. Besides the observation of equal 

 numbers of true-breeding individuals in every 

 type suggests the theory so pointedly that it 

 may be laid hold of specially Avith advantage. 

 Mendel's statement then becomes : — 



i. Pure species j^roduce pure-breeding 

 forms. 



They must therefore 1)e furnished with the 

 materials for doing so. 



ii. Hybrids also produce pure-breeding 

 forms. 



Therefore they also must l)e furnished with 

 the materials for doing so. 



iii. Hybrids produce equal numl)eis of pure- 

 breeding individuals in every type. 



Therefore they must ))e furnished with equal 

 numbers of the materials for the production of 

 the characters borne l)y their true-breeding, 

 progeny. 



Next month we shall discuss the ex])erimentSr 

 by which Mendel proved his theory. 



