MORPHOLOGY. 65 



green, foliaceous, or even producing buds like that itself ; 

 whilst in other cases they become coloured, less firm, and 

 harsh in texture, so that no true limit can be placed be- 

 tween them and the next stage, the calyx, which in 

 some cases resembles the bracteae, whilst in others 

 again the true leaves themselves. In the corolla a con- 

 siderable change is generally seen not only in the for- 

 mation, but in the colour of the appendage ; sometimes 

 the series may be traced down through corolla, calyx 

 and bractese, to leaf, all three rising so gradually from 

 their type that it is impossible to mark the commence- 

 ment of either; at other times the petals have been 

 known to be like the leaves themselves. At the next 

 stage of the series of morphological development, the 

 change into stamens is to be seen ; sometimes the pas- 

 sage of the petals into these organs is evident, whilst in 

 others, though but rarely so, their conversion into their 

 type, the green leaf, has been known. At the last or 

 concluding change the pistilla are evolved, and in many 

 flowers the relationship these bear to the leaf is dis- 

 tinctly observed : their conversion into petals, folia- 

 ceous expansions analogous to the sepaloid pieces of 

 the calyx, and even into the green leaf itself, have been 

 recorded ; and though their transition into the next 

 descending form, the stamen, is rare, yet the latter has 

 been known to produce ovula. 



7. But it may be asked whether the existence of 

 one organ in the place of another undeveloped, or even 

 the partial change of one structure into that of another, 

 is sufficient to allow us to say that a common plan of 

 arrangement is to be seen or allowed in such abnormal 

 or undeveloped structures, when normally evolved, as is 

 seen in the organ here assumed as their type, and which 

 sometimes exists in lieu of them. 



8. In the vegetable, as in the animal kingdom, 

 there is only one force regulating the development 



G3 



