io8 THE COTTON PLANT IN EGYPT chap. 



sequences is to stimulate the belief which lies dormant in 

 the minds of most people — practical and otherwise — 

 namely, that all man-made plant varieties suffer from an 

 innate perversity, due to their " un-natural " origin, which 

 causes them to "revert" at the first opportunity, and so 

 to revenge themselves on human interference. 



Up to the present point we have considered only the 

 zygotic constitution of the " variety," and have merely 

 laid emphasis on the fact that when a " variety " of cotton 

 plants is inspected, plant by plant, the component 

 individuals are not usually identical ; we have seen, in 

 addition, that the differences between nominal varieties 

 are mean differences, which are negligible in most 

 morphological characters, slight in physiological characters, 

 and are definite only in respect to the nature of the 

 commercial product — the lint hairs. 



Our analysis has now to be driven much deeper. We 

 have to investigate the origin of these zygotes, to ascertain 

 whether they are derived from identical gametes or not, 

 and to determine what effect their constitution may have 

 on succeeding generations. 



Gametic impurity. — In the older writings on plant- 

 selection we find continual references to " transmitting 

 power," coupled with advice to test this power by 

 examining offspring. The reasons for this precaution 

 are now better understood ; "transmitting power" is not 

 a mysterious vital function, but can be reduced to 

 formulae. The causes of difference in this respect are 

 two-fold. 



In the first case, the plant originally selected may ha^'c 

 been an extreme fluctuation and its offspring will 

 therefore regress to the mean. 



In the second case, with which we are now concerned, 

 the original plant was heterozygous, derived from a natural 

 or artificial hybridisation. Such hybridisation might have 

 taken place in the previous year — the plant thus being an 



