122 



TAXONOMY. 



is changed into cellular texture and fat ; or the common mem- 

 brane of the vessels into the substance of bone. But in plants 

 this change takes place the more readily, the nearer the organs 

 stand to one another in the process of formation ; so that the 

 roots may become stem and branches, — these again may be 

 changed into roots, — leaves may become leaf-stalks, and the 

 reverse, — the calyx may become corolla, and the filaments 

 may change to petals ; and even in some cases the fruit may 

 again push out leaves, and from the receptacle new branches 

 may spring up. 



183. 



In the formation of one part from another. Nature pro- 

 ceeds in such a way, that she first renders the parts compact 

 and simple, when she intends to give them an extended and 

 compound form. The root-leaves are naturally more simple 

 than the following stem-leaves, and these again are the sim- 

 pler the nearer they stand to the flower. When hindrances 

 to this compacting of the part occur, the consequent exten- 

 sion must also undergo a change, and hence we see many al- 

 terations arise. 



184. 



These alterations, when we attend to the substance of the 

 part, may be arranged under the five following classes. 



1. The parts become prickly, as happens in the branches 

 of Fruit-trees, — the stipulse of the Acacia, — ^in innume- 

 rable leaves, — in the calyx even, — and, in one instance, 

 the Cerviera De Cand. a genus of the family of the Ru- 

 biaceae, in the petals of the corolla. 



^. The parts become lengthened out into a flexible fibre, 

 which, when it is curved, is usually called cirrhus. It 

 is well known, that the leaf-stalks of Vetches, and of the 

 species of Lathyrus, are thus extended into cirrhi ; as 

 also that the flower-stalk of the Vine and of the Passion- 

 flower uniformly undergo this alteration. The transi- 

 tion of the stipulae in Smilax, and of the nerves of the 



leaves in Flagdlaria apd Nepenthes, into cirrhi, is less 



2 ' 



