CHAPTER XII 



THE LAWS OF HEREDITY THEIR 



DEFINITE MEANING AND 



INTERPRETATION 



IT is traditional that one cannot gather grapes 

 from thorns nor figs from thistles. The tra- 

 dition embodies, by implication, the essence 

 of the great central laws of heredity. This law is 

 stated even more explicitly in the colloquial 

 phrase "like produces like.' 7 



The sum and substance of the matter is that 

 each and every living organism, be it vegetable or 

 animal, tends to reproduce its own kind, and if we 

 would get at the fundamental laws of heredity we 

 have but to follow up the clew that this familiar 

 fact gives. 



We may see the principle illustrated to best 

 advantage, perhaps, if we consider the lowly 

 single-celled organisms, of which bacteria furnish 

 a familiar type. These creatures, observed under 

 the microscope, are seen to multiply by division, 

 a single bacterium splitting to form two bacteria, 

 each of which presently grows to the dimensions 

 of the original parent, and then repeats the proc- 

 ess of division. 



Such a process of multiplication obviously 

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