META:\IORriIOSES OF PLANTS. 99 



very often found resuming the appearance of common 

 leaves if any thing occurs to interfere with their in- 

 tended structure hefore it is entirely fixed. Thus we 

 find leaves in the place of petals, or as they say petals 

 metamorphosed into leaves, in some kinds of double 

 Tulips ; sepals and pistils often changed to leaves in 

 double Roses ; all the parts of the flower turned into 

 leaves in other plants ; and a multitude of similar 

 cases with which the Botanist is acquainted. You 

 will find all this so fully demonstrated in my Intro- 

 duction to Botany, Book vi., or in other works of a 

 like nature, that there is no doubt of the fact ; and the 

 doctrine is now the foundation of modern views of 

 the real structure of flowers and fruit. It is not my 

 plan to enter into such questions in these letters, but 

 I could not avoid calling your attention to the cir- 

 cumstance. 



Now mark the practical application of this know- 

 ledge. If the parts of the flower are only leaves 

 in a particular state, any of those parts in which 

 veins can be discovered will serve to shew the ar- 

 rano-ement of the veins as well as the true leaves 

 themselves. In the Pink the petals are fully ex- 

 panded, and full of veins ; they are therefore fitting 

 objects to examine ; and their structure wiU tell us 

 whether the Pink is Exogenous or not. You will 

 find them distinctly netted, and thus that question is 

 set at rest. 



This then, which is an Exogenous plant, has oppo- 

 site undi'S'ided leaves seated on the swoln joints of the 

 stem. The calyx consists of a tube composed of five 



