124 



INTRODUCTION TO CYTOLOGY 



deletions, and inversions (Chapter XVIII). The same is doubtless also 

 true of many other species in which a "typical" or "standard" chro- 

 mosome set has been described. 



In Datura stramonium there are 12 chromosomes in the set. These 

 vary somewhat in different races. In "line lA " there are one very long, 

 two long, five large medium, two small medium, one short, and one very 

 short members. ^^ According to Lewitsky, all 12 may be distinguished 

 on the basis of size, arm ratio, and the presence of small rounded 

 segments. In Pisum sativum the seven pairs in the root cells are distin- 

 guishable^^ (Fig. 67, A). In Vicia faba there are five pairs with subter- 



Fig. 67. — Somatic chromosome complements in various higher plants. A, Pisum 

 sativum. {After Lewitsky, 1930.) B, C, Crepis capiUaris, after regular treatment and 

 after shortening by cooling. (After Delaunay, 1930.) D, Allium allegheniense, with 

 translocated fragment on one member. {After Levari, 1932.) E, Najas major. {After 

 Tschernoyarow, 1914; see also Midler, 1912, Winge, 1927a, and Takamine, 1927.) F, 

 Nicotiana alata var. grandiflora. {After Avery, 1929.) 



minal spindle-attachment regions and one much larger pair with a 

 median attachment region and a conspicuous "secondary constriction^^ 

 (Fig. 61). The chromosome set of Crepis capiUaris (= virens) consists 

 of a large chromosome with its attachment region between the middle 

 and end, a medium-sized one with very unequal arms and a satellite, and 

 a small one with unequal arms. Hence the somatic cells show three 

 distinguishable pairs ^^ (Figs. 69; 72, B). In Nicotiana alata var. grandi- 

 flora the nine pairs of chromosomes fall into five classes on the basis of 

 their morphology (Fig. 67, F). 



In a large number of plants and some animals the chromosome com- 

 plements of gamete and zygote do not have merely one set and two sets of 



1^ Belling and Blakeslee (1922 el seq.), Blakeslee, Belling, Farnham, and Bergner 

 (1922), Lewitsky (1930, 1931a). In much of the literature on Datura the term "set" 

 is used rather for any group of homologous chromosomes, a diploid plant having 12 

 "sets" of two, a triploid 12 "sets" of three, and so on. 



"Lewitsky (1930), Marshak (1931). 



" Sharp (1913, 1914a), Sakamura (1914, 1915, 1920), Maeda (19306). For other 

 species of Vicia, see Sweschnikowa (1927a6, 1928, 1929). 



IS Rosenberg (1909a, 1918, 1920), de Smet (1914), Collins and Mann (1923), 

 Mann (1925), M. Nawaschin (1925afe, 1926), W. R. Taylor (1925c), Hollingshead 

 (1930c), Lewitsky and Araratian (1931). 



