TRANSACTIONS OF WAGNER 

 50 



MENDEL AND HIS LAW 



terminal bush, unless crossed, that is, unless fertilized with those of another 

 kind, always come terminal. 



One more series of experiments gave him another characteristic in which 

 his peas followed the now well-estabKshed law. When he crossed pole peas with 

 dwarf peas, the resultants were always tall, never dwarf, but in the succeeding 

 generation they came in both kinds, there being three tall plants to one dwarf. 



Accordingly, in peas, round is dominant and wrinkled recessive: yellow- 

 ness of seed is dominant over greenness; green seed coats are dominant over 

 brown; swollen seed pods are dominant over constricted; pods green when 

 unripe are dominant over pods yellow when unripe; the axillary position of 

 flowers is dominant over the terminal, and tallness of stalk is dominant while 

 dwarfness is recessive. 



The next step taken by Mendel was to find what would happen when he 

 crossed plants which differed in two of the above-mentioned particulars. Ac- 

 cordingly, he took a yellow round pea and crossed it with a green wrinkled 

 pea. As the reader will expect, all the seeds in the next generation were 

 round and yellow. In the second hybrid generation, however, he got 



315 seeds, round and yellow (9) 



10 1 " wrinkled and yellow (3) 



108 " round and green (3) 



32 " wrinkled and green (i) 



A little inspection will show that these numbers are very close to the 

 proportion of 9, 3, 3, and i. At first it is difl&cult to see the law underlying 

 this, though the simplicity of the numbers arouses suspicion of a law, but if we 

 look at one quahty, one at a time, we will find that there are twelve round peas 

 to four wrinkled, which is as three to one, and there are twelve yellow peas to 

 four green, which again is as three to one. In other words, whether we deal 

 with one pair of qualities at a time or with two pairs, each pair behaves as if 

 it was alone. 



He now attempted crossing seeds which differed in three of these striking 

 aspects, and while he found that the result grew apparently more complicated, 

 in reality it was just as simple, and each pair of qualities was behaving as if it 

 were alone, entirely unaffected by the presence of the other qualities. 



Mendel's great contributions to our ideas of heredity are : First, plants are 

 mosaics of unit characters, each of which can be inherited independently of 



