CHAPTER III 



THE task that Mendel set before himself was to 

 gain some clear conception of the manner in which 

 the definite and fixed varieties found within a species 

 are related to one another, and he realised at the 

 outset that the best chance of success lay in working 

 with material of such a nature as to reduce the 

 problem to its simplest terms. He decided that 

 the plant with which he was to work must be 

 normally self-fertilising and unlikely to be crossed 

 through the interference of insects, while at the 

 same time it must possess definite fixed varieties 

 which bred true to type. In the common pea 

 (Pisum sativum} he found the plant he sought. 

 A hardy annual, prolific, easily worked, Pisum 

 has a further advantage in that the insects which 

 normally visit flowers are unable to gather pollen 

 from it and so to bring about cross fertilisation. 

 At the same time it exists in a number of strains 

 presenting well-marked and fixed differences. The 

 flowers may be purple, or red, or white ; the plants 

 may be tall or dwarf; the ripe seeds may be yellow 

 or green, round or wrinkled, such are a few of the 



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