NATURAL CLASSIFICATION. 133 



known. Even the petals of the Strophanthus De Cand. 

 and the filaments of Hirtella resemble twisted threads. 



3. The usual fibrous or rounded form of particular parts, may 

 also become of a leafy nature, and thus conceal their ori- 

 ginal form. The branches of Phyllanthus, and even of 

 the Cactus species, are of a leafy structure ; and, in the 

 former, the flowers seem to be set on the margin of the 

 leaves, whilst it is only the expanded and leafy flower- 

 stalks which bear them. We have already remarked, 

 that the nerves of the leaves of some species of Poly- 

 trichum are fashioned into lamellae. In the same man- 

 ner, it is not unusual for the filaments to expand them- 

 selves, and, in the Irideae, even the pistils from this ex- 

 pansion assume the appearance of petals. 



4. Parts that are naturally green and juicy, often become 

 dry and membranaceous {scariosus). This is most fre- 

 quently observed in the calyx-scales of compoimd flowers, 

 and in the calyx of the single florets, which we consider 

 as a pappus. 



5. Lastly, It very often happens, that membranaceous or 

 leafy parts become fleshy, as we every day see in the re- 

 ceptacle of the Strawberry and Raspberry. Thus, also, 

 the one-seeded berries of the Anonese unite by the swell- 

 ing of the receptacle into a single juicy fruit ; and, in 

 like manner, the strobilus of the Juniper, by the swell- 

 ing of the scales and their union, takes the form of a 

 juicy berry. In the Hoveniu dulch-, even the flower- 

 stalk, after the time of blossoming, becomes juicy, well 

 flavoured, and of a beautiful red colour. 



C. On the Ufiion of Organs. 



185. 



Every person knows that there are instances in which two 

 fruits, two branches, and even two trees, are united with one 

 another. But there is a law of nature which regularly pro- 

 duces this junction ; namely, when similar organs have a dis- 

 position not only to hang together, but whvu they cannot pro- 



