INTERCHANGE 341 



certain constant characters in each species. He found the 14 

 chromosomes in a diploid (Enothera were always associated at 

 diakinesis and metaphase end-to-end in rings of two, four, six or 

 other even numbers, up to fourteen. The size and number of the 

 rings were constant for each species, except that occasionally a chain 

 or two chains might replace a ring ; just as with the simple pairs 

 which usually form rings in other organisms with median centro- 



FiG. 105. — First meiotic division in (Enothera muricata with a ring of 

 fourteen chromosomes. Above, at diakinesis (showing the self- 

 interlocking of the ring, cf. Ch. VII). Below, at first metaphase 

 (showing a dis junctional arrangement which gives regular 

 segregation of the two complexes). X 4000 (from D., 1931 c). 



meres and complete terminalisation [cf. Catcheside, 1933), a rod is 

 formed owing to the failure of one of the two chiasmata. 



The same constancy is found in the hybrids and mutants as well, 

 and Tables 54 and 55 show some of the results that have been 

 obtained. 



Cleland found that the ring of chromosomes usually arranges itself 

 so that adjoining chromosomes go to opposite poles (Fig. loi). He 

 assumed that the chromosomes had a fixed position in the ring, so 

 that in a ring of fourteen, each of the seven chromosomes of one 



