THE ANGIOSPERMAE 



1 107 



pression, an interesting example being the transformation of a perianth 

 consisting of two trimerous whorls into one pentamerous whorl by the 

 fusion of a member of the outer whorl with one of the inner. In some other 

 cases suppression certainly occurs, for example in Raminciihis aiiricomus, 

 and Anemone nemorosa, where partial or total suppression of the perianth 

 may be observed, in varying degree, even among flowers on the same plant. 

 Pleiomery is a natural consequence of chorisis, but it may also result 

 from the reduction in size of organ rudiments, which permits larger numbers 

 to be formed in a given space on the receptacle. Meristic variations of either 

 kind may occur either sporadically within the limits of a single species or as 

 a constant feature distinguishing whole species or genera from those most 

 nearlv related to them. 



A B 



Fig. 1079. — Contanuii paliistre. Diagrams of three flowers showing pleiomery of the pos- 

 terior stamen of the inner whorl causiiig change from pentamery to hexamery. {After 

 Goebel.) 



An instance of the first kind is the variation in the number of stamens in 

 Potent ilia {Comarum) palustris (Fig. 1079). The posterior stamen of the 

 antisepalous whorl sometimes divides into three and this is associated with 

 chorisis of the opposed sepal and the intercalation of a new petal, thus 

 transforming a pentamerous flower into a hexamerous one. This exempli- 

 fies the point that meristic variation is seldom confined to a single organ, 

 but seems to aflFect whole sectors of the receptacle, in which growth is either 

 increased or decreased, relative to the other sectors, with corresponding 

 eft'ects on the numbers of the parts included in those sectors. Salisbury has 

 examined large numbers of flowers in certain genera of Ranunculaceae, 

 e.g., Erant/u's, Ficaria and Anemone (Fig. 1080), in which meristic variation 

 is very prominent, and has shown that there is a decided correlation between 

 the numerical condition in difl^erent parts of the flower, increase or decrease 

 in numbers being, in general, exhibited simultaneously by the perianth, 

 androecium and gynoecium. Branching of stamens and carpels and lobing 

 of the petals illustrate the' tending to multiplication by fission. Only^in 

 the case of the corolla is there evidence of increase occurring by the trans- 

 formation of other floral organs, in this case of the stamens. 



