The Aneuploids 347 



ploick were louml: these were either 4ii deficient or 1/; phis one 

 chromosome.^** Among hctcroi)loids in Nicotiana, deficient types 

 (2;/ — 1) Hke those in Datura were found. Simihirfy, in Enira sativn 

 the ]jhint was facking two chromosomes, 2// — 2. No explanation 

 difierent from that ad\anced for Datura has been made. The devia- 

 tion originated when colchicine acted on somatic mitosis. 



In \iew of these cases we are prompted to suggest that the sub- 

 type of exploded c-metaphase, the distributed c-metaphase, shoidd be 

 studied further with respect to unecpial distributions of chromosomes 

 following treatment with colchicine. Activity of this type was often 

 observed in pollen tubes of Polygonatu)ii . but the relation to such 

 phenomena has been for the most part overlooked. As a basis for an 

 action of colchicine on mitosis that leads to numbers other than the 

 true i)olvploids, illustrations are abundant in cultures of pollen tuf:)es 

 Avhich account for a variety of deviating numbers that might occur 

 ^\■hen colchicine acts on mitosis. 



14.2: Mixoploidy From Colchicine 



The action of colchicine upon individual cells was emphasized in 

 the first studies with Allium roots. .\ single root tip treated for 72 

 hoius may yield cells with many chromosomes while other cells re- 

 main dipioid. It has been confirmed many times that within one 

 meristematic group there may remain diploid cells alongside tetra- 

 ploids. Such tissues are described as mixoploid. These cases should 

 not be confused with sectorial chimeras since the word means mixed 

 together. 



A cyto-histological study of maize after treatment with colchicine 

 showed that different areas may become tetraploid more readily than 

 others.^i Treatment of maize plants with colchicine rarely gives rise 

 to a completely tetraploid plant.*^ Certain branches of the tassel show 

 tetrai:)loid. and others, diploid pollen. ^Vhether these are true sec- 

 torial chimeras or the result of mixoploid conditions has not been 

 decided. 



Another case of mixoploid tissues from treated plants was fol- 

 lowed through enough generations to prove that mixoploids were 

 involved rather than sectorial chimeras. =^ Lolium pereuue L., 2/? = 

 14. was originally treated by subjecting seed to colchicine. -^ Plants 

 with tetraploid cells, determined by measurements of pollen grains 

 and chromosomal counts in root tips, were isolated. Sujjposedly tetra- 

 ploid tillers were being separated and transplanted. Also some clones 

 were separated as progenitors for control diploid clones. Selections 

 -^vere again made for diploid and tetraploid clones.-^ As before, 

 chromosomes were coiuited. For two generations such propagation 

 was continued, yet mixoploid tissues persisted into the seventh gen- 



