DUAL CONTROL 



59 



Genoiijpic Ckan ^^e 



i^ y\ /^ Tradescani-ia 



J^ ^ Phragmahhia 



and 

 Constnchon 





r / 



A 



Crepis 

 Ascsr/s 



Fig. 14, 



S^•r^c^^raI Cfian ^^e 



Fragme/if'ahon ( ^ ^ /^r Crepis 



M ffctorum 



yV y*/V ^'^^^ Cracca 



^ techrum 



Tra/ts/ocah'on 



De/, 



icienc i/ 



Interchan ge J J i 



Crepis 

 dioscoridis 



Maithiola 



Zea 

 Ma^s 



Fig. 15. 



Figs. 14 and 15. — Diagram to show the kinds of change produced 

 genotypically and structurally in the chromosomes. In Ascaris, 

 genotypic control determines a structural change. 



of its parts at all stages ; and (iv) the normal separation of its 

 halves to opposite poles at anaphase. The last two are determined 

 by the activity of the centromere which, having its own organisa- 

 tion, reacts in its own way to special conditions in the cell. 



