CHORISIS OR DEDUPLICATION. 



253 



fore the other ; an arrangement which is not known to occur in 

 the leaflets of any compound leaf. 



458. Some examples of this vertical or transverse chorisis may 

 be adduced before we essay to explain them. A 



common case is that of the crown, or small and 



mostly two-lobed appendage on the inside of the 



blade of the petals of Silene (Fig. 302) and of 



many other Caryophyllaceous plants. This is 



more like a case of real dedoublement or unlining, 



a partial separation of an inner lamella from the 



outer, and perhaps may be so viewed. The sta- 

 mens sometimes bear a similar and more striking 



appendage, as in Larrea for example (Fig. 303), 



and most other plants of the Guaiacum Family ; also in the Dodder 

 (Cuscuta, Ord. ConvolvulaceaB). Let it be noted that 

 in these cases the appendage occupies the inner side 

 of the petal or stamen, and that it is often two-lpbed. 

 Again, before each petal of Parnassia (Fig. 305), al- 

 though slightly if at all united with it, is found a body 

 which in P. palustris is somewhat petal-like, with a con- 

 siderable number of lobes, and in P. Caroliniana is di- 

 vided almost to the base into three lobes, which look 



much like abortive stamens. The true stamineal circle, however, 



occupies its proper place 



within these ambiguous 



bodies, alternate with the 



petals. We cannot doubt 



that the former are of the 



same nature as the scale 



of the stamens in Larrea, 



and the crown of the pet- 

 als of Silene. 



459. It may also be 

 noticed, that, while in col- 

 lateral chorisis the in- 

 creased parts are usually all of the same nature, like so many sim- 



FIG. 302. A petal of Silene Pennsylvania, with its crown or appendage. 



FIG. 303. A stamen of Larrea Mexicana, with a scale-like appendage cohering with its 

 base on the inner side. 



FIG. 304. Diagram (cross-section) of the flower of Parnassia Caroliniana. 305. A petal, 

 with the appendage that stands before it. 



22 



