162 BOTANY. [CHAP. v. 



occupying the top or youngest portion of the stem, the 

 four whorls being, in every primitive flower, separated 

 by very short internodes. In the common field butter- 

 cup, which illustrates a simple and uncomplicated type 

 of flower, we meet with, commencing from below, a 

 calyx composed of five leaves or sepals, springing inde- 

 pendently from the stem, and perfectly free from each 

 other; such a calyx is termed polysepalous. Next we 

 come to the corolla, consisting of five yellow petals also 

 growing directly from the stem, and quite free from 

 each other hence called polypetalous. Within the 

 corolla, and consequently an internode higher up the 

 stem, is situated a considerable number of stamens, each 

 of which originates directly from the stem ; and finally, 

 at the tip or apex of the stem of the flower, we find a 

 number of closed leaves or carpels, each containing a 

 single seed, springing independently or free from each 

 other, from the tip of the floral axis ; the carpels collec- 

 tively form the fruit, and a fruit composed of free carpels, 

 that is, not grown to each other, is said to be apocarpous. 

 The above indicated sequence of development of the 

 four whorls constituting a flower is in reality the only 

 one that exists in the flower, but owing to the subse- 

 quent growing together of the components of any one 

 whorl, or of the different whorls with each other, we 

 meet with flowers exhibiting such different structural 

 peculiarities and appearances from those presented by 

 primitive types, as the buttercup, that unless the transi- 

 tions from one to the other are clearly traced, it is 

 difficult to realize that the two are built on the same 

 plan. If the flower of the primrose is next examined, 

 the sepals will be found cohering together and forming 



