RARE FORMS OF FERNWORTS.-XVI. 



onoclea sensibilis f. obtusilobata and allied 

 Forms. 



The history of the vicissitudes that have attended 

 upon that form of the sensitive fern known commonly 

 as obtusilobata, ever since its discovery, is a most in- 

 teresting commentary upon the progress of botanical 

 knowledge in general, while it also throws consider- 

 able light upon the fudamental processes concerned in 

 the production of such forms. The form mentioned 

 was described by Torrey in the "Flora of New York" 

 as a variety of Onoclea scusibilis and in his day was 

 regarded much as we now regard sub-species. In- 

 deed, many botanists considered it distinct enough to 

 be a separate species and Schkuhr so described it under 

 the name of Onoclea obtusilobata. We are all disin- 

 clined to give up an opinion once we make it our own, 

 however, and long after it was shown that it was not 

 a species, we clung to the idea that it was a good "va- 

 riety." Now it is well-known to be a mere form that 

 can be produced at will by anyone who cares to take 

 the trouble. 



The possibility of making exact experiments in the 

 production of the form, lies in the fact that Onoclea 

 sensibilis is not only a dimorphic species but seasonally 

 dimorphic as well. The two sorts of fronds are about 

 as different in appearance as two leaves from the same 

 plant could well be, the coarse ample sterile fronds be- 

 ing simply pinnate or with the lower pinnae again 

 pinnatifid, while the fertile are completely bipinnate 

 with the pinnules rolled up into close little balls which 

 enclose the sori. Not a few students are wont to con- 

 sider these berry-like objects as the spore cases, but 

 careful examination, when the fertile fronds are young, 



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