METAMORPHOSIS. 



153 



much enlarged, white -co loured, sterile, and often 

 slightly zygomorphic. The same type of corolla may, 

 in abnormal cases, as in the snowball-tree (V. OjjuIu* 

 var. sterilis), extend to all the inner flowers, so that 

 the inflorescence is sterile throughout; the flowers 

 composing it are, however, hardly zygomorphic, or 

 only slightly so. This is comparable, so far as the 

 change in the corolla is concerned, to the " doubling " 

 of the Chrysanthemum-heads. 



Camus* observed, in the already zygomorphic 

 flowers of Viola odor.ata, that this feature was accen- 

 tuated by the reduction of the two posterior petals to 

 quite small, ligulate organs. Penzig points out the 

 interest of this as lying in the fact that this character 

 of the posterior petals is the normal one in the genera 

 Anchietea, Corynostylis, and some species of Ionopsi- 

 dium of the same order. 



All cases in which either the corolla as a whole, or 

 the individual petal, undergoes a change from the 

 actinomorphic or a simple form, to the zygomorphic or 

 a more complex form, represent a progressive pheno- 

 menon. 



On the other hand all cases of simplification of the 

 flower, as when the zygomorphic changes into the 

 actinomorphic, as when a perianth-leaf loses its spur 

 or its otherwise highly differentiated shape, must be 

 regarded as reversions. 



Staminody. — This phenomenon is perhaps not quite 

 so common as one might expect. A good case is that 

 mentioned and figured by De Candolle in the shep- 

 herd's-purse (Gapsella Bursa-pastoris) , in which, in 

 place of the usual six, there were ten stamens ; the 

 four extra stamens were the outermost, and occupied 

 the place of the absent petals, being due to their 

 transformation (PI. XLIII, figs. 1 and 2). 



Battandier observed in some very closely sown, and 

 therefore etiolated specimens of Pupavev walraeflorum, 

 that the flowers had only two narrow petals, the 



* Camus' paper has not been seen. 



