PEDIGREE 9 



The subsequent evolution of the fuzz and lint which 



all the three main groups of the genus possessed from the 



commencement is hest sketched in terms of 



Evolution im it-factor composition, as ascertained by 



of Fuzz. J 



the application of Mendel's law.* 



The fuzz in the Asiatic cottons appears to depend on a 

 single factor, which may be lost, and naked-seeded sports 

 or varieties then appear. In the Peruvian and Upland groups 

 there are certainly two factors concerned at least, the loss of 

 one of them producing a seed with fuzz almost entirely con- 

 fined to the two ends of the seed, and the loss of the other or 

 of both producing an entirely naked seed. The appearance of 

 naked-seeded forms, such as Hindi Weed, within the Upland 

 group, and possibly of naked seeds within Upland varieties 

 themselves, would seem to be due to the modern loss of one 

 factor; while the typical naked or semi-naked seed of the 

 Peruvian group, which is older than history, seems to be 

 due to the loss of the other factor far back in evolutionary 

 history. How far this generalization may go can only be 

 settled by much laborious accumulation of data from the 

 study of hybrids, but it is certainly true in some cases, such 

 as a first cross of naked Hindi Weed with the semi-naked 

 Egyptian, which is covered with fuzz like Uplands, and 

 behaves in later generations in such a way as to show clearly 

 that two factorial elements are involved. 



The history of the fuzz seems thus to be one of analysis, 

 the full fuzz of the primitive cotton being progressively split 

 up into simpler forms by the loss of factors. That of the lint 

 is certainly the reverse, new forms appearing by synthetic 

 evolution,! first bearing lint in place of no lint at all, and then 



* A general outline of this subject is given in " Mendelism," 

 by Professor R. C. Punnett. London, 1911. 



+ The appearance of lint, or an increase in its length, may be 

 interpreted as analytical evolution, if the author's views on 

 growth-inhibition are substantiated. 



