STOUT: DUPLICATION AND COHESION 485 



should be the case it is evident that while the susceptibility is very 

 decidedly limited to the variety it can be transmitted directly or 

 indirectly though incompletely to large numbers of the offspring of a 

 hybrid generation. 



Summary 



An unusual type of fasciation occurs in the variety of chicory known 

 as red-leaved Treviso. It consists of a very decided duplication in 

 the main axis of the stem, giving two stem-elements with, however, a 

 decided cohesion of the two. In this variety of chicory there are also 

 various irregularities in the development of cotyledons and plumule. 

 All degrees of fusion between the two cotyledons are in evidence; in 

 some seedlings only one cotyledon is present. Occasionally no plu- 

 mule develops. 



The character of duplication and cohesion of the main axis is 

 strongly but not completely heritable. There is wide variation in 

 the degree of duplication and a few plants with a normal unduplicated 

 main axis occur. 



In an Fj hybrid generation of crosses between plants with dupli- 

 cation and plants of wild stock which exhibit no tendency to such 

 fasciation the character of duplication is incompletely dominant both 

 as to degree of expression and number of plants affected. An inter- 

 mediate type is strongly in evidence in which the only indication of 

 duplication is seen in a mixed and irregular phyllotaxy. 



EXPLANATION OF PLATE XII 



Nos. 1-9 inclusive are of stems of plants of the variety red-leaved Treviso; 

 no. 7 is of the 1915 crop, all others are of the 1916 crop. 



No. I. Stem showing no duplication. Phyllotaxy regular. 



No. 2. No duplication but stem thicker than in no. i. Phyllotaxy regular. 



No. 3. Stem of small plant. Short segment of duplication at a. 



No. 4. Duplication from a to b; phyllotaxy above a is irregular with tendency 

 for branches to be paired. 



No. 5. Very decided duplication from a to b. Lesion separates the two stem- 

 elements in lower center.- Stem-elements parallel below but twisted above. 



No. 6. Decided duplication with parts much twisted. 



No. 7. The two stem-elements separate from the base. No lesions. 



No. 8. Longitudinal lesions strongly developed. One stem-element much 

 contorted. 



No. 9. Much torsion with transverse lesion of one stem-element. 



Nos 10, II and 12 are Fi hybrids of red-leaved Treviso X unfasciated plant of 

 a wild variety. 



No. 10. Duplication evident in lower two thirds of stem. 



No. II. Duplication indicated by a very slight but broad groove near base. 

 Phyllotaxy mixed and irregular especially near base. 



No. 12. No duplication. Phyllotaxy regular. 



