No. 645] ASSORTMENT OF CHROMOSOMES 34S 

 TABLE III 



Chromosomes of Progeny of Triploid Datura Pollinated by Diploid 



The number of normal progeny shown in Table III is 

 much beyond expectation (on the hypothesis that orienta- 

 tion of trivalents in the first division of the megaspore 

 mother-cell is random), even if we allow the excessive 

 total of over 4,000 ovules to 3 capsules. Detachment of 

 chromosomes in the megaspore-mother-cells to the max- 

 imum extent found in the pollen-mother-cells will only 

 partially account for this excess. Similar results were 

 obtained by van Overeem with triploid (Enothera bien- 

 nis pollinated by the normal (9). 



Triploid Inheritance.— The 75 progeny showed triploid 

 or trisomic (not disomic) inheritance (2) of two probably 

 independent pairs of genes, those for purple and white 

 flowers, and those for prickly and smooth capsules. 



Distribution of Extra Chromosomes. — Among the 33 

 plants with one extra chromosome, cases were found 

 where this extra chromosome was estra large, large, 

 medium, small, or extra small. These plants showed 11 

 bivalents and 1 trivalent at the late prophase and early 

 first metaphase. Ten different forms were recognized by 

 external features among 30 of the 33 forms with an extra 

 chromosome. ( Three plants have not yet been identified. ) 

 Among these ten forms, 1 form (Globe) occurred 5 

 times, 3 forms (Buckling, Ilex, and Reduced) occurred 4 

 times, 2 forms (Glossy and Elongate) occurred 3 times, 

 3 forms (Rolled, Cocklebur, and Poinsettia) occurred 

 twice, and 1 form (Microcarpic) occurred once. The ex- 

 pectations for each of 12 possible forms are presumably 

 equal, namely 2.5. The Datura plants with 2 extra 



