334 



INTRODUCTION TO CYTOLOGY 



distribution differs significantly from a random one, which indicates 

 some influence favoring one type of orientation in the spindle rather than 

 the other. What it is that thus affects the distribution is not yet known. 

 As observations multiply it will doubtless be found that the ratio of the 

 various types of distribution varies widely in different cases. 



(Enothera. — The genus (Enothera has occupied a prominent position 

 in genetics ever since de Vries formulated his mutation theory largely 



..,ii>. 



mm 



UWt ■ 



./ 



\i 



H 



'.V 



Fig. 191. — Stages in meiosis in the microsporocytes of (Enothera. A-D, CE. francis- 

 cana: A, prophase showing a ring of 4, and 5 pairs. B, diakinesis, after separation of pairs 

 from the ring. C, metaphase of /. D, anaphase, showing regular distribution. E-H, 

 (E. franciscana sulphurea: E, prophase showing ring of 12 and one pair. F, alternate 

 chromosomes in the ring of 12 passing to the same pole in anaphase; single pair not shown. 

 G, later stage; all chromosomes shown. H, anaphase of division //, with 8 chromosomes 

 in one figure and 6 in the other; this is due to an occasional irregularity of distribution in /. 

 (After Cleland, 1922, 1924.) 



on the basis of the peculiar genetic behavior of (E. Lamarchiana. Not 

 only did this species give rise to occasional "mutants," but it displayed 

 a number of other genetical peculiarities for which little by way of explana- 

 tion was available. It was soon found that the Onagra section of the 

 genus was peculiar cytologically, the chromosomes in meiosis forming 

 rings or chains with various numbers of members in the different species.^ 



5 Gates (1907 et seq.), Lutz (1907 et seq.), Geerts (1907-1911), B. M. Davis (1909- 

 1911), Cleland (1922 et seq.). Later works: S. H. Emerson (1924a, 19286, 1931a6), 

 Boedijn (1924, 1926), Oehlkers (1926), HEkansson (1926o, 1928a, 19306c, 1931c), 

 Valkanover (1926), Kihara (1927a), Sinoto (1927), Sheffield (1927, 1929), Schwemmle 

 (1924 et seq.), Gerhard (1929), Kulkarni (1929a6c), Gates and Sheffield (1929a6), 

 Illick (1929, 1932), Leliveld (1928, 1931), Weier (19306), Cleland and Oehlkers 

 (1929, 1930), Catcheside- (1930, et seq.). Gates and Goodwin (1931), Darlington 

 (1929a, 1931e), and Hedayetullah (1932). For general accounts of research in 

 (Enothera, see Lehmann (1922), Oehlkers (1924), Renner (1925), and Gates (1928). 



