1928] 



Soiling shead : CJiromosomal Chimeras in Crepis 



345 



plates observed. Plate 54, figures a and h, shows the chromosome com- 

 plexes with surrounding- areas from the outer cortex in comparable 

 regions of the diploid and tetraploid roots. Each of the chromosomes 

 of the diploid complex could be recognized in the tetraploid and the 

 longest one of the set could be identified four times in the best tetra- 

 ploid plate. Undoubtedly there has been a doubling of the diploid 

 set. An examination of plate 54 shows that the average size of cells 

 and nuclei is larger in the tetraploid root. 



Fig. B. A cross-section of root of biennis-setosa hybrid derivative showing 

 the extent of the tetraploid area. The outer ring is the extension of the root cap 

 and contains no dividing cells. 



The occurrence of two tetraploid roots in the same plant may be 

 taken as evidence that part of the central cylinder from which 

 branches arise had become tetraploid. It was thought possible that 

 the plant above ground might have been affected similarly, and if so, 

 the pollen produced on a tetraploid branch would be larger than that 

 on a diploid. Examination of pollen from various branches, however, 

 showed no noticeable size differences, so it was concluded that tetra- 

 ploidy was probably confined to the roots. 



In this same plant a root was examined which contained a number 

 of large cells. Most of them were clearly multinucleate, from two to 

 four nuclei having been counted in single cells (pi. 55). Plate 55 h 

 shows one of the smallest of these with 2 nuclei, and 2 nuclei may be 

 observed in one of the cells in a. In the larger cells nuclei were to be 

 found in successive sections. These cells were scattered throughout 



