508 Mutations 



and towards the autumn, when all those of the 

 first group are faded away, and only a weak 

 though large section of the heads is still flower- 

 ing, the whole aspect of the variety gradually 

 retrogrades. The same law of dependency and 

 periodicity is prevalent everywhere. In my 

 own cultures of the unproved field-marigold I 

 have observed it frequently. The number of the 

 ray-florets may be considered as a direct re- 

 sponse to nourishment, both when this is deter- 

 mined by external circumstances, and when it 

 depends on the particular strength of the 

 branch, which bears the head in question. It is 

 a case exactly similar to that of the supernumer- 

 ary carpels of the pistilloid poppy, and the de- 

 ductions arrived at with that variety may be 

 applied directly to double flowers. 



This dependency upon nourishment is of high 

 practical importance in combination with the 

 usual effect of the doubling which makes 

 the flowers sterile. It is a general rule that the 

 most perfect flowers do not produce seed. At 

 the height of the flowering period the external 

 circumstances are the most favorable, and the 

 flowering branches still constitute the stronger 

 axes of the plants. Hence we may infer that 

 sterility will prevail precisely in this period. 

 Many varieties are known to yield only seeds 

 from the very last flowers, as for instance some 



