636 Mutations 



general rule that in the higher plants side 

 branches are situated in the axils of leaves. 

 Bracts are reduced leaves, but the spikes of the 

 cruciferous plants were formerly devoid of 

 them. The flower-stalks, with naked bases, are 

 seen to arise from the common axis at indefinite 

 points. 



Hence the inference that crucifers are an ex- 

 ception to a general rule, and that they must 

 have originated from other types, which did 

 comply with this rule, and accordingly were in 

 the possession of floral bracts. Or, in other 

 words, that the bracts must have been lost dur- 

 ing the original evolution of the whole family. 

 This conclusion being accepted, the accidental 

 re-apparition of bracts within the family must 

 be considered as a case of systematic atavism, 

 quite analogous to the re-appearance of the 

 scapes in the acaulescent primrose. The sys- 

 tematic importance of this phenomenon, how- 

 ever, is far greater than in the first case, in 

 which we had only to deal with a specific char- 

 acter, while the abolition of the bracts has be- 

 come a feature of a whole family. 



This reversion is observed to take place ac- 

 cording to two widely different principles. On 

 one hand, bracts may be met with in full devel- 

 opment, and in a few stray species, assuming the 

 rank of a specific character. On the other hand 



