190 Observation of the Origin of I'arictics. 



"iven rise immediatelv to flowerheads with central li""ii- 

 late florets if it had been on a sufficiently large scale. 

 But it would not have produced them in a proportion 

 which could be predicted l)v Quetelet's law, but accord- 

 ing to the principles of discontinuous variation which 

 are still unknow'n to us. 



The course of the improvement is different in the 

 two cases. The results obtained with the maize conform 

 to the law of regression, the increase in the number of 

 rows in the ears becoming slower and more difificult to 

 secure, the further we get from the starting-point. Ex- 

 actly the reverse is the case in the Chrysanthcnnini. The 

 i:>rogress was continuous and did not materially change 

 until 1899, when the first central ligulate florets appeared. 

 Then it took a leap, all the offspring of this plant having 

 more or less double flowers. More strictly speaking, 

 the leap had already taken place, the plant with the first 

 central ligulate florets (Fig. ZZ) having already crossed 

 the threshold. Its offspring behaved like the offspring 

 of a pure race, such as for instance C. inodoruni plcnis- 

 simnm. 



A break therefore occurred, and obviously before 

 1899; either in tlie origin of the seeds of 1898 from 

 which the plant in question arose, or even earlier. 



And since C. inodornni plenissinuun has maintained 

 itself for many years without selection, it is probable 

 that the new C. scgctnni plenum will do the same. But 

 the reverse was the case with the maize which reverted 

 to the old form within a few years after the cessation 

 of selection (Vol. I, p. 125). 



Hitherto I have taken the number of ray-florets in the 

 terminal inflorescence almost exclusively as a character 

 of the whole plant, and the curves have been plotted 



