ZH 



4N 



2N 4-16 2N + 26 



4N •»- I 6- 



4N + 26 



4N -f- 36 



2N 



2N + 21 • 22 



2N+23-24 2N + 21- 22 + 23-24 



t 



2N + 1-2 2N + I -I 



2N + 2 • 2 



2N + 17 



2N t 



17 



Plate A. Capsules of Datura, to illustrate dosage. — Above are the diploid and tetraploid 

 capsules. In the next row are a series illustrating the effects of different dosages of the so- 

 called "Globe" chromosome (chromosome ends 21 and 22); notice the increase in effect 

 with increasing dose relative to the rest of the genotype. The third row shows the normal 

 capsule, with two primary trisomies (for chromosomes 21-22 ( Globe) and 23-2^) for 

 comparison with the double tnsomic which contains three of both 21-22 and 23- 24-: note 

 that this combines the globular shape and thin spines of the two primaries. In the lowest 

 row, at the left is the primary for 1-2 for comparison with the two derived secondaries 

 which have an extra chromosome consisting of two 1-ends or two 2-ends; note how each 

 of the secondaries shows an exaggeration of some of the characteristics of the primary. At 

 the right of the row are shown the secondary with extra 17-17, and the tertiary with 

 extra 2.17, which is to some extent intermediate between the 2-2 and 17-17 secondaries, 



(Courtesy of A. F. Blakeslee.) 



