MEIOSIS AND lEUTILITY IN POLYPLOIDS 



in one line or in a convergent V. With convergence tv^o cliromo- 

 somes go to one pole and one to the other; with linearity the middle 

 chromosome may go to either pole or it may be left behind and 

 act as though it had been unpaired. Univalents either divide late 

 at the first division and their daughters lag and arc lost in the 

 cytoplasm at the second; or they lag and are lost at the first; or 

 again they are included without division in one of the daughter 

 nuclei at the end of the first division as though they were daughter 

 bivalents; or even, as we saw, they may misdivide. 



TABLE 12 



A. CHROMOSOMES OF POLLEN GRAINS IN SAMPLES 

 TAKEN UNDER FAVOURABLE (F — 502 GRAINS), AND 

 LATE SEASON OR UNFAVOURABLE (U — 116 GRAINS) 

 CONDITIONS, FROM TRIPLOID CREPIS CAPILLARIS 

 Ox = 9). (FROM DATA OF CHUKSANOVA, 1939) 



B. PROPORTION OF THE EXTRA FREQUENCY PER GRAIN 

 (0-5) ACTUALLY FOUND FOR THE THREE EXTRA 

 CHROMOSOMES, A, C AND D 



Note: "Loss" is the deficiency of the mean with respect to the binomial ex- 

 pectation. As in Hyacinthus, it is highest for the shortest chromosome because this 

 forms fewest chiasmata and therefore fewest trivalects. 



As a rule the different trivalents orientate themselves at random 

 with respect to one another on the fi.rst m.etaphase spindle. In con- 



T-3 



