272 Gates. 



which I called lata rubricalyx are of even greater interest, for they 

 combine with the rubricalyx pigmentation the peculiar foliage and 

 habit of the mutant lata. The de Vriesian lata is practically devoid 

 of red pigment in every part, while these plants showed a conspicuous 

 amount of red in every organ. 



Probably all these four mutants contained 15 chromosomes 

 instead of 14, since this number is found in all pure individuals both 

 of lata and scinilata examined. The presence of 15 chromosomes in 

 the lata rubricalyx plant examined fm"nishes the final and conclusive 

 proof that a change in the constitution of the nuclei has taken place, 

 and that mutation is a process in which germinal changes occur 

 independently of hybrid recombinations. Furthermore, these two 

 independent processes may go on side by side in the same germ cell 



Several years ago (Gates, 1908) I formulated the hypothesis that 

 the mutations in Oenothera arise from changes in the constitution 

 of the germ cells which are occasioned in part at least by irregularities 

 in the chromosome distribution during meiosis. It is difficult to imagine 

 how a more crucial confirmation and proof of this hypothesis could 

 be obtained than by such facts as I have here described. Most critical 

 students of Oenothera have been agreed in interpreting the mutation 

 phenomena as due to actual germinal changes and not mere recom- 

 binations of characters, but it has remained for the cytological investi- 

 gation of these forms to supply the final proof. That proof in the case 

 of lata and semilata (15 chromosomes) and gigas (28 chromosomes) 

 is now complete as regards tlie independence and interpenetration 

 of hybrid and mutation phenomena. 



The difference between the nuclear constitution of lata or setni- 

 lata and Lainarckiana from which they arise, is quite as definite as 

 that between the nuclei of the males and females among insects having 

 sex chromosomes. And just as, in insects having an accessory chromo- 

 some, duplication of that chromosome is associated with the deve- 

 lopment of female sex organs, so in 0. lata the extra chromosome, 

 which must evidently be a triplicate of a pair already present, is 

 associated with the appearance of the lata foliage and habit. 



I am indebted to Professor J. B. Farmer, F. R. S., for several 

 suggestions and criticisms of this paper. 



IV. Summary and Conclusions. 



Briefly recapitulated, this paper contains the following results 

 and conclusions: 



