42 STRUCTURE AND LIFE-HISTORY OF HAY-SCENTED FERN. 



DISCUSSION OF RESULTS. 



We have restricted ourselves thus far to mere description of the develop- 

 ment of Dennst&dtia punctilobula. It remains to point out in order some 

 general considerations suggested by the investigation. 



TAXONOMY. 



Whether our fern belongs in the Cyatheacese or the Polypodiacese should 

 not be difficult to decide. The principal differences between the orders 

 may be shown by a table: 



CYATHEACESE. POLYPODIACE^;. 



Annulus a complete circle, oblique. Annulus surrounding three-fourths of spo- 



Antheridium cover multicellular. rangium, symmetrical. 



Cushion of prothallus with bristles. Antheridium cover unicellular. 



Broad cells in continuous series in the rhi- Cushion without bristles. 



zogenous line. Rhizogenous cells separated by smaller 



cells. 



In all of these points the plant now under discussion agrees with the 

 Polypodiaceae. But Bauke (1876) states for Dicksonia rubiginosa that 

 its antheridium is cyatheaceous. Moore (1857) and recent writers place 

 D. rubiginosa Kaulf . and Dicksonia punctilobula Willd. in the genus Denn- 

 sttzdtia. Gwynne-Vaughan (1903) further shows that D. rubiginosa has a 

 complicated solenostelic stem. If Moore and his followers are correct, 

 the character of the antheridium must cease to stand as a distinction 

 between the two orders. This point is much in need of investigation 

 in other Dicksonias and Dennstaedtias, as well as in Davallia, Lindsay a, 

 Microlepia, and the allied genera. Cyatheaceous root-structure I have 

 observed in Cibotium regale. But we need to know the arrangement of 

 rhizogenous cells in the other genera just named. A knowledge of these 

 points is especially needed for the Melanesian Z^wste^m flaccida, the type 

 of the genus. For it may yet develop that our North American fern is 

 not referable to the same genus with D. flaccida. In that case we should 

 have to adopt the generic name Sitobolium Desv. The point can only be 

 settled after a careful examination of D. flaccida throughout its structure 

 and life-history. The removal of our fern from the genus Dicksonia 

 L'Herit. is generally agreed upon, and is quite sure to stand. The use of 

 the name Dicksonia certainly leads to confusion, as when a recent European 

 writer speaks of our plant as a " tree-fern. " : But further studies along 

 the lines indicated are needed to fully establish the position. Indeed, it is 

 not impossible that such a comparison would break down the feeble barrier 

 between Cyatheaceae and Polypodiaceae by showing a series of connecting 

 links. 



*"Den nordamerikanischen, 2-5' hohen Baumfarn." Brick, 1897. 



