STOUT: DUPLICATION AND COHESION 483 



instead of one, accompanied by their cohesion or incomplete separation. 

 In both the factor of cohesion is present, but in the cotyledons it leads 

 to reduction in the number normal to the species, while in the stem it 

 tends to reduce the duplication to the single stem-element that is 

 normal to the species. 



The occurrence of the sort of duplication described above has now 

 been observed in four generations. Thirty-five plants of the 1913 

 crop of the variety red-leaved Treviso were grown from commercial 

 seed. In 14 plants the main axes were decidedly duplex, the length 

 of the segments showing duplication ranging from a few inches to 

 about three feet. The stems of the other 21 plants showed no sign 

 of duplication. All plants of this generation which were tested were 

 found self-sterile from physiological incompatibility, so it was not 

 possible to obtain self-fertilized seed. Numerous crosses were at- 

 tempted between plants, but only one cross attempted was compatible. 



In 1914, 12 plants were grown as progeny of the cross between two 

 plants which were quite alike in exhibiting duplication of rather inter- 

 mediate development. In all 12, duplication developed. The vari- 

 ability in degree of duplication was marked and ranged from very 

 slight indications to very decided cases of torsion and lesion. One 

 plant developed too late in the season to be tested for self -fertility, 

 but the other ii were all self-sterile. However, some compatible 

 crosses were made from which 43 plants were grown in 19 15. 



Of the 1915 crop, 39 of the 43 plants exhibited duplication to some 

 degree. In one plant the two elements were completely separate from 

 the very base upward (no. 7). In several plants torsions and lesions 

 were strongly developed. Four plants were apparently not in the 

 least fasciated and in each of these the phyllotaxy was regular and 

 single. 



In the 1916 crop, 150 plants were grown. Two of these were from a 

 self-fertile plant (the only one of the 1915 crop that was found to be self- 

 compatible in any degree). The 148 other plants of this generation 

 were from six different crosses involving eight different parent plants, all 

 of which, however, exhibited duplication in some degree. This genera- 

 tion was descended from three generations of parentage that exhibited 

 duplication. There was duplication to some extent at least in 144 of 

 these plants. Six appeared to have a single stem-element with regular 

 phyllotaxy; these six plants were distributed among the offspring of 

 three different crosses. 



One plant of the 1916 crop exhibited a noticeable fasciation of the 

 ribbon type in the upper branches in addition to duplication and 

 cohesion in the main axis. The tips of the main branch and of various 

 laterals were broadly flattened and the branching was reduced so that 



