INTRODUCTORY 7 



derived from a living source. There is no such thing as 

 spontaneous generation known to scientific men. Life 

 under present conditions is always derived from life. 

 The processes of fission or of budding suggest merely the 

 increase in number of living things without any change 

 in quality ; and in practice the offspring of budding 

 is found to repeat, as a rule, very exactly, the characters 

 of the original organism from which the bud sprang. 

 In Plants this fact is made use of by horticulturalists. 

 Roses are propagated by "budding"; strawberries by 

 "runners " ; apples, pears and plums by " grafts," which 

 are each of them parts of an original plant removed and 

 encouraged to grow on as new individuals. These retain 

 the exact qualities of colour, scent, and flavour of the 

 original stock, though not necessarily the size, or season 

 of maturity. But it is different with the offspring pro- 

 duced by the sexual method. The fact that it is a blend 

 of two parental characters at once distinguishes it from the 

 result of mere fission or budding. The sexually produced 

 offspring is not a mere repetition of either parent. In the 

 fusion of gametes there is a mechanism which provides 

 for a summation of parental characters from both parents. 

 But it is a matter of common observation that the sexually 

 produced offspring does not repeat all the characters of both 

 parents. The later Lectures of the series will take up the 

 question how the characters that are inherited are dis- 

 tributed in the sexually produced offspring. And as many 

 of the Higher Plants and all of the Higher Animals, 

 including Man himself, are sexually produced, it will be at 

 once seen how large a question is here involved. For 

 sexual propagation is not a mere matter of increase in 

 number, but one which touches the very springs of 

 Evolution and of Progress in Living Beings. 



