84 American Fern Journal. 



P. acrostichoides, but the lower part is considerably 

 narrower than that species. The sterile fronds prob- 

 ably approach more closely Dryopteris cristata in general 

 outline. The pinnae are extremely variable in shape, 

 approaching P. acrostichoides on one hand and D. 

 cristata on the other, but are usually pinnate, On large 

 fertile fronds, the lower pair or two are pinnate through- 

 out their length as are most of the contracted spore- 

 bearing pinnae. Practically all the pinnae are pinnate 

 next to the rachis both above and below the midrib. 

 That above the midrib is the largest, suggesting the 

 auricled portion of P. acrostichoides. Many of the 

 pinnae on the fertile fronds are indented at the outer 

 end, showing a tendency to bifurcate, and are widest 

 two-thirds or three-fourths of the distance from the 

 rachis. The sterile fronds are usually beset with spines 

 at the ends of the pinnules. In many of the fertile 

 fronds, only the lower one to three pairs of spore-bearing 

 pinnae develop, giving the frond the appearance ot 

 having been broken or bitten off at an early stage. The 

 sori are usually intermediate in number between those 

 of the parent species, but approach both in different 

 fronds. In a few cases, sori appear on the pinnae below 

 the contracted portion. The indusia in a few instances 

 show traces of a sinus. 



Last winter the writer found, a short distance above 

 Great Falls on the Virginia side of the Potomac, a fern 

 that appeared to be a peculiar form of the common 

 Christmas fern. Wishing to investigate this, a second 

 trip was made to the locality, late in May, and three 

 large healthy plant- were found in company with a 

 great number of typical P. acrostichoides, and with 



several plants of I), cristata growing a few feet distant. 



It took but a single glance to arrive at the conclusion 

 that the plants were hybrids. The detailed examina- 

 tion show I an admixture of characteristics in every 



