220 THE SEED-VESSEL AND ITS KINDS 



leaf half green half eolonred, either in the flower or on 

 the stalk just below it. Jlnemone alpina produces occa- 

 sionally a petal among^ the segnunts of its involucrum 

 or bractea. Geum rivale^ Engl. Bot. t. 106, when 

 cultivated in dry gravelly ground, exhibits such trans- 

 formations in abundance. Between petals and sta- 

 mens there is evidently more connection, as to their 

 nature and functions, than between any other organs, 

 and they commonly flourish and fall together. Yet 

 only one instance is known of petals changing to sta- 

 mens, which Dr. Withering has commemorated, in 

 the Black Currant, Rihes nigrum. On the other hand, 

 nothing is more frequent than the alteration of stamens 

 to petals. Here then the metamorphosis begins to be 

 retrograde, and it is still more so in the Cherry above 

 mentioned, by which we return to the herbage again. 

 — The line of distinction seems to be most absolute 

 between stamens and pistils, which never change into 

 each other ; on the contrary, pistils, as we see, rather 

 turn into petals, or even into leaves. 



5. Pericarpium. The seed vessel, extremely various 

 in diflferent plants, is formed of the germen enlarged. 

 It is not an essential part, the seeds being frequently 

 naked, and guarded only by the calyx, as in the first 

 oid».^rofthe Linn an class Didynamia, of which Lai- 

 miuin Engl. Bot. t. 768, and Galeopsis, t. 667, are 

 examples ; also in the great class of compound flow- 

 ers Syngenesa, as well as in Ihimex, t. 724, PolygOf^ 

 num, t. 989, the Umbelliferous tribe, numerous 

 Grasses, &,c. 



