FLUCTUATING VARIATIONS. 



23 



In the second generation of this hybrid every one of the eight possible 

 combinations of these three pairs of characters was found, as follows: 



Serial No. 



Leaf color. 



Fruit color. 



Fruit shape. 



1 



Green 



Yellow 



Round. 



Pear-shaped.- 



Round. 



Pear-shaped. 



Round. 



Pear-shaped. 



Round. 



Pear-shaped. 



2 



Green 



Yellow 



3 



Green 



Red 



4 



Green 



Red 



5 



Yellowish 



Yellow 



6 



Yellowish 



Yellow 



7 



Yellowish 



Red 



8 



Yellowish 



Red 









Two of these eight types were like the original parent varieties, the 

 other six were new. This case illustrates well the power a knowledge 

 of the law of recombination puts into the hand of the breeder. Breed- 

 ers have unconsciously used this law since breeding first became an 

 art, but a knowledge of the principles involved now enables them to 

 accomplish desired results much more quickly and surely than was 

 formerly the case. 



FLUCTUATING VARIATIONS. 



From what has been said concerning the law of recombination it 

 is easy to see that in a species which naturally cross-fertilizes in the 

 field we are continually getting new combinations of hereditary char- 

 acters. For instance, in a cornfield hardly any two plants can be 

 found that carry exactly the same combination of hereditary charac- 

 ters. If we should take a single grain of corn and plant it where it 

 can not cross-fertilize with another its progeny would break up into 

 types somewhat as shown in Table II, except that, instead of stopping 

 with twenty-seven different types, each of these would be subdivided 

 into three others, and each of these again subdivided in the same way, 

 and so on within the limits of the number of separate and independ- 

 ent hereditary characters for v/hich the grain we started with was 

 heterozygote. Generally speaking, only a comparatively few of these 

 characters will be important to the breeder, so that the others may 

 be neglected. But we must not overlook the fact that in the main 

 the remarkable fluctuations of characters seen in a cornfield are due 

 to this recombination of characters from year to year. On the other 

 hand, if we take a single grain of wheat and plant it, then save every 

 seed of it for planting, the plants produced in the second generation 

 would, ordinarily, be exactly alike in so far as their combinations of 

 hereditary characters are concerned. This is because under ordi- 

 nary field conditions wheat is self -fertilized, and a field of wheat in the 

 main consists of plants that are completely homozygote with re.fer- 

 ence .to every one of their hereditary characters. When we do get 



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