34 



BOTANICAL GAZETTE 



[JANUARY 



original pinnae; and if we lay a well-developed pinna of the Pierson 

 fern by the side of a small frond of the Boston fern, we shall be 

 struck with the fact that they are almost identical. In short, the 



Fig. 2. — Pinna of Pierson fern. 



pinnae of the new variety are transformed from the original condi- 

 tion in such a way that the plan of the whole frond of the Boston 

 fern is now seen in the primary segments of the Pierson frond. 



The completeness of the 

 imitation may be indicated 



still further: 



i. 



The 



pinnae are 



elon- 



Fig. 3.— Growing apex of pinna of Pierson 

 fern (left) and Boston fern (right). 



gated, the growth being less 

 strictly determinate than that 

 of the original pinnae, and 

 more like that of the frond. 



2. The apical growth of the 

 pinnae is now circinnate, as 

 shown in fig. 3, after the 

 fashion of the original frond. The pinnae of the Boston fern on 

 the other hand, while lapped together in the young state at the 

 summit of the developing frond, are not in the least circinnate. 



3. The blades of the pinnae are divided. 



4. The outline of the pinnules is like that of the original pinnae. 



5. Finally, the peculiarity of the original form, that its pinnae in 

 age become disarticulated by the development of an absciss-layer, 



