80 
Sudden Appearance and Constancy. 
grandiflora, B. bipinnata, and B. atropurpurea are well- 
known species with ray florets. B. trlpartlta and B. 
cermta are very common in Holland and I have often 
tried to find or to obtain examples with ligulate florets, 
Fig. g. Senecio Jacobaea discoidcus, KOCH. 
but as yet in vain. By this fact both forms are proved 
to be constant as thoroughly as a proof can be. In other 
countries, however, the varietates radiatae are known to 
