The Aneuploids 351 



When numerous periclinal chimeras were demonstrated among 

 well-known varieties of apples, interest was again intensified because 

 the breeding behavior dejiended upon the specific chromosomal nature 

 of a ])articular chimera. i'^- i" If the layer that produced pollen was 

 dijjloid, triploid, or tetraploid, then entirely dilferent results in hy- 

 bridization could be expected. Periclinal tetraploid giant sports of 

 Mcintosh should be of great interest since tetraploids in subepidermal 

 layers breed on the tetraploid level. i*"' Some important varieties are 

 trijjloid, many are dij^loid, while some sports are chimeras. Two 

 naturally occurring chimeras in apples are: (1) the 2-4-2 type and 

 (2) the 2-2-4. 



The pomological curiosit) known as "sweet and sour" from the 

 Rhode Island Greening is meaningfully interpreted as a periclinal 

 chimera. The sour portion originates from the outer layer and the 

 third layer, whereas the sAvect ])ortion takes its origin from the second 

 layer.1'5 



Seven years after colchicine treatment, a Mcintosh tree bore fruit 

 that was giant-like, and similar to the diploid-tetraploid periclinal 

 sport which occurs in nature. The induced type proved to be a peri- 

 clinal chimera. By adventitious buds that originate from deeper 

 layers, a com])lete tetraploid stock can be obtained. When crossed 

 ^vith diploids, this becomes breeding material for new triploid vari- 

 eties. AVith better knowledge of periclinal chimeras, breeding in 

 many fruit trees can be expected to advance. 



Another kind of chimera is the sectorial chimera. As the name 

 imjilies. sectors are either diploid or tetraploid. The changes occur 

 in a mass of cells not limited to layers. This type was studied in 

 Datura.'' One branch becomes tetraploid and another diploid, de- 

 pending on the origin of a specific branch.'^ ' 



The A\ ide distribution of periclinal chimeras in polyploids derived 

 from colchicine shows that the change is not unusual. \Vhile our 

 discussion is limited to only a few species, important work has been 

 done with Lilium, Solanurn, and many other plants. The principles 

 as outlined with fruits and Datura are basic to all chimeras. 



14.4: Sex Determination and Polyploidy 



As was stated in the introduction to this chajner, jiolyploidy and 

 special j^roblems in botany did not arise suddenly \\hen colchicine 

 became known for its use in research. At this time, however, there 

 was an inmiediate increase in papers dealing with such problems. A 

 notable case was the relation between sex and polyploidy in plants.-"*-^^ 

 One mav erroneously conclude that new ideas were conceived as soon 

 as colchicine was discovered. A proper persj^ective is needed here 

 to e\aluate projicrly the role played by an imj^roved methcxl such 

 as colchicine proved to be. Whether the colchicine technique had 



