360 W. J. C. Lawrence Cytoic^ia 2, 



D. variabilis 



The garden dahlia has 64 somatic chromosomes. I have dealt in 

 detail with chromosome association in this species in a previous paper 

 (1931). Briefly, about 3 or 4 ring quadrivalents and occasionally one 

 sexivalent are found at diakinesis. The bivalents are conspicuously 

 preponderant. At metaphase bivalents, quadrivalents and sexivalents 

 occur, and in addition every degree of secondary association between 4, 

 6 and 8 chromosomes (Fig 3 6, c). Both types of association (multi- 

 valent and secondary) often persist into second metaphase and it was 

 at this stage that Ishikawa first noted the association of bivalents in 

 Dahlia. 



Hidalgoa Wercklii. 



This plant was previously reported by me to have about 31 chromo- 

 somes in somatic cells. P.M.C. counts have since definitely shown the 

 number to be 30. 



A remarkable feature of metaphase I is the size differences between 

 the bivalents and the marked association of bivalents of similar size 

 (Fig. 4). Groups of 4 are common and groups of 6 have been seen. 

 Hidalgoa is being studied further. 



a b n^^ 



thf^ .Kyi :••*•• 



d e • 



Fig. 4. 



Fig. 4. Meiosis in Hidalgoa Wercklii (2n=30) 

 polar views MI. Note size differences of groups, e. Mil. 



