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COLLEGE BOTANY 



somes of the nuclei (see page 129) and may be briefly explained 

 as follows: The nucleus contains chromatic material from 

 both parents. When the cell divides, the maternal and 

 paternal chromatin appear to organize separately and therefore 

 each maintains its individuality in the offspring. Although the 

 cells may receive an equal amount of chromatic material, they 

 do not necessarily receive the same characters. Since the parents 

 bear not tvs'o but a great many characters, the number of possible 

 combinations are enormous. It has been 

 demonstrated that more than 100 pairs of 

 characters adhere more or less closely to 

 the Mendelian Law^s. 



DeVries. — This well-known Dutch 

 scientist (Fig. 112) extended and ex- 

 plained a great deal of the work of his 

 predecessors. By growing pedigreed plants 

 and studying them through many genera- 

 tions, he demons'trated that there were two 

 kinds of variations, the continuous and dis- 

 continuous, and finally brought forth the mutation theory. The 

 continuous variations are the very common but. very slight 

 variations which are very generally recognized by every one, such 

 as those in size and color of the individual fruits from the 

 same tree, of leaves from the same plant or of seeds from the 

 same plant. The variations are within certain limits and it is 

 doubted if any one of them gives rise to any well-defined type. 

 The discontinuous variations are known as mutations; they 

 arise suddenly, are well defined and persist in succeeding gen- 

 erations, thus giving rise to new types.. It was formerly 

 believed that many of the great number of varieties of our 



Fig. 112. — Hugo DeVries. 



