No. 645] ASSORTMENT OF CHROMOSOMES 341 



Daturas by pollen from normals, 4 triploid plants have 

 resulted (3). Their somatic formula is shown to be 3(L+ 

 41 + 3M + 2m + S + s). Similar results have been ob- 

 tained for triploid hyacinths by de Mol (7). 



Attraction of Homologous Chromosomes. — In the nor- 

 mal Daturas the late prophase or early metaphase of the 

 first division in the pollen-mother-cells shows 12 sets with 

 two united chromosomes (bivalents) in each (Fig. 3). 

 These bivalents can readily be arranged in the six size 

 classes. In the corresponding stage of the triploid 

 Daturas there are 12 sets of three united chromosomes 

 each, and these trivalents can be arranged according to 

 the size formula (Fig. 4). Sometimes two of the three 

 rod-shaped chromosomes are united together at both 

 ends, and the third is joined on at one end only, or the 

 three may form a hook (Fig. 5). Some trivalents were 

 seen by Osawa in triploid mulberries (8), and a group of 

 9 trivalents was also found in a triploid Canna (1). (The 

 complete group of 9 trivalents has also been seen in 4 

 other triploid Cannas.) 



i ^ ♦ * «- 



Separation {Disjunction) of Chromosomes.— So far as 

 seen in Datura, two chromosomes usually pass to one 

 pole, and one chromosome to the other, from each triva- 

 lent, as is the case in triploid Cannas (1). 



Assortment of Chromosomes. — From one triploid 



