HETEROPLOIDY 341 



unbroken series may be somewhat exceptional, but series with two 

 or three members are very common, especially in the angiosperms. 

 Extremely high multiples are found occasionally, as in Prunus laurocera- 

 sus with about 176 somatic chromosomes (ca. 22 X 8)^ and Senecio 

 Roherti-Friesii with about 180 {ca. 36 X S).*^ Euchlcena mexicana has 10 

 pairs of chromosomes and is annual, while E. perennis has 20 and is 

 perennial; the same is true of Sorghum sudanensis and S. halepensisJ 





* 



A ^ B 



D 



#tt 



/\\^1 #•*?# ^•^^'^^^ ^z\^^^ 



#^^^^ •^•^•#1 ••.••^-.^ ••**^r 



/A:;-::- .:v.V;5 o;r:.;: v ;-::• 

 ;r.t:.\* v-vJi» •*-'>'• •.•.•'.*//.'. 



• /•;.* V/V/* v»tV ••;•:••♦* 



Fig. 194. — The chromosomes in the metaphase of the first meiotic mitosis in the micro- 

 sporocytes of various species of Car ex, illustrating aneuploidy. A, pilulifera, 9 chromo- 

 somes. B, sparsiflora, 16. C, montana, 19. D, tomentosa, 24. E, digitata, 26. F, 

 loliacea, 27. G, caryophyllea, 29. H, punctata, 34. /, distans, 37. /, vesicaria, 41. K, 

 Goodenoughii, 42. L, hirta, 56. (After Heilborn, 1924.) 



A striking example of aneuploidy within a genus is afforded by Carex, 

 in which the species examined show 22 gametic numbers, all but one of 

 which lie between 9 and 42 (Fig. 194). Taxonomic relationship is roughly 

 indicated here by the number and size of the chromosomes.^ Another 

 example of such marked aneuploidy is Scirpus.^ Heilborn thinks it 

 probable that this exceptional condition is connected with the peculiar 

 mode of pollen formation in Cyperacese. Frequently a genus shows two 

 or more euploid series, or it may have euploid combined with aneuploid 



5 Meurman (192%). 



« Afzelius (1924). 



' Longley (1924o, 1932); see also Huskins and Smith (1932). 



« Heilborn (1922, 1924, 1925, 1932). 



9 Hakansson (19285), Hicks (1928). 



