AT THE PERIOD OF PUBERTY. 159 



to say, where the development of the main stem and 

 branches of the plant are suddenly arrested by the meta- 

 morphosis of the leaf-buds at their summit into flower- 

 buds, no such gradual metamorphosis in the leaves is to 

 be seen ; and this makes the task of identifying the flower- 

 leaves with the ordinary green leaves of the stem far more 

 difficult. Yet even here we are not without indications of 

 that common family relationship which subsists amongst 

 all the leaf organs. There is the same rudimentary condi- 

 tion of the floral axis which we observe amongst the com- 

 mon green leaf clusters on the branchlets when their 

 vegetative powers are enfeebled ; the same spiral arrange- 

 ment ; for, if we consider the leaves of the flower carefully, 

 we shall find that they alternate with each other, the sepals 

 or leaves of the calyx occupying an intermediate position 

 between the petals. We observe, also, that these floral 

 leaves deviate more widely from the ordinary type of stem- 

 leaf, in proportion as they are situated toward the superior 

 portion of the axis ; this change of structure increasing as 

 the vegetative forces become enfeebled. Thus, whilst the 

 sepals or leaves of the calyx retain almost all the characters 

 of leaves, these characters are less apparent in the petals 

 and stamens, until finally, in the carpels, or pistils, which 



The different parts of a flower : a, the calyx ; b, the corolla ; c, the 

 stamens j d, the pistils. 



occupy the summit of the axis, the departure from the 

 ordinary leaf-type is the widest. 



Transitional forms, between sepals and petals, and be- 



