region it is west and southwest, along Bay Creek it is almost east, and near Wallace 
School it is east of south, Elevations are almost the same, Mohlenbrock & Voigt 
(1959) give the elevation of the Steagall site as 560 feet above sea level, I did not 
checkthe elevations ateach locality by measurements from the nearest bench marks, 
but an examination of the topographic maps shows that in the seven other sites filmy 
fern grows at an elevation between 540 and 580 feet, 
Light intensity may be an important control inthe growthof the fern. Shaver 
(1954) observed that the destruction of trees and the consequent opening of the forest 
canopy destroys the fern, Forest destruction may partially account for the dimi- 
nution of the fern at the Steagall site. Much of the Americanbeech, Fagus grandifolia 
Ehrh., has been or is being removed in Jackson Hollow as a forestry measure to 
permit a better growth of tulip tree, Liriodendron tulipifera L, Such a measure in 
Jackson Hollow could spell doom to two stands of filmy fern in Illinois. Jackson 
Hollow should be maintainedas a nature preserve because of this fern andother rare 
= 
Fig. 12,--Gigantic overhang in the north section of Jackson Hollow, At the base of the cliff grow 
three sizable patches of filmy fern, The two figures near the center of the picture serve as a scale to show 
the size of this overhang, 
12 
