112 



PRINCIPLES OF PLANT-TERATOLOGY. 



(PI. XXXIX, fig. 1) ; the sepals are also free in the 

 same way. The harebell (G. rotundifolia) has been 

 found in the wild state with polypetalous flowers. 

 Certain of the Ericaceae, e. g. Rhododendron, RJtodora, 

 Erica, occasionally exhibit a polypetalous corolla; this 

 is not a surprising fact when Ave know that several 

 genera of the order Ericaceae possess this character 

 normally, e. g. Pyrola, Clethra, Leiojihyllum, Ledo- 

 thamnus, Cladothamnus, Elliottia ; so that, so far as 

 this particular feature is concerned, these genera stand 

 nearer to the ancestral form. 



In the flower of Stapelia, previously described, in 

 which an extra corolla appeared, the normal corolla 

 was dialypetalous : a rare phenomenon in the Ascle- 

 piadaceae. 



In double flowers, where fresh petals are added from 

 the andrcecium or are intercalated independently, it 

 frequently happens, as in Nerium Oleander and Caly- 

 stegia piibescens mentioned by Goebel, that, not only 

 the newly-added petals but the normal ones as well, 

 are polypetalous from the first. This is due, probably, 

 to correlation of growth ; we can understand that if 

 the normal corolla had remained gamopetalous it would 

 tend to cramp and hinder the expansion of the flower 

 caused by the addition of new petals, while the poly- 

 petalous condition would not do so. 



Celakovsky observed a most interesting variety of 

 Anthemis austriaca in which the ray-florets were not, 

 as in the normal form, ligulate, but bilabiate (PI. 

 XXXIX, figs. 7 and 8). As is shown by the nervation, 

 the normal ligulate corolla, in spite of having a tri- 

 dentate apex, really contains within itself all five petals. 

 This is proved beyond all doubt by the organization 

 of the floret in the variety, in which two lateral upper 

 petals have become detached, and in many cases 

 constitute an upper lip. The chief interest of this 

 abnormality lies in the fact that the bilabiate character 

 of the ray- florets is the normal feature in one section 

 of the Compositae (Labiatifloras) to which the Mutisieae 



