D. J. SCOURFIELD ON MENDELI8M AND MICROSCOPY. 



generations in regard to two of the pairs of characters, for live 

 generations for two other pairs, and for four generations for the 

 remaining three pairs. Hybrids, whether of the firsl or any 

 subsequent generation, always gave rise to three kinds of 

 progeny in approximately definite proportions— namely, one 

 pure dominant, two hybrids (looking like pure dominants), and 

 one pure recessive. 



Put into the form of a diagram, the foregoing results appe 

 quite simple, though none the less remarkable : — 



D x R ... ... ... Parents (dominant and re 



I sive). 



D(E) Hybrids (all dominant in ap- 



I pearance, but all containing 



j — | the recessive character;. 



D D(R) D(R) R... Progeny resulting from the self 



fertilisation of the hybrids — 



namely, three dominants to 



D D(R) D(R) R D D(R) D(R) R R each recessive. Two of the 



apparent dominants, how 



*\ 



ever, as shown in the next 

 generation, contain the re- 

 cessive character, and are 

 therefore hybrids like : 

 parents. The other dominant, 

 and likewise the recessive, 

 are pure, and remain constant 

 indefinitely. 



Going a step further, Mendel next showed that even when two 

 or more pairs of characters are associated in the same cross, the 

 above rules hold good for each pair considered independently of 

 the others. Thus, if one of the parent plants possesses all domi- 

 nant characters (the dominance being previously ascertained by 

 testing each pair of characters separately), then the hybrids pro- 

 duced wall entirely resemble that parent, and not the other. If, 

 on the other hand, the parent plants each possess a number of 

 dominant and recessive characters, then the hybrids will not 

 resemble either parent exactly, but will be of an intermedia 

 nature, owing to their exhibiting all the dominant characters of 

 both parents, but none of the recessive character-. In the next 

 and later generations, obtained as before by self-fertilisation ol 

 the plants, the number of forms produced becomes somewhat 

 complicated, but can be calculated exactly by combining t 

 formula 1:2:1 (or, for outward form only, 3 : 1 ) as many tin 

 as there are pairs of characters involved. 



