The Habitats of the Pellaeas 



T 



By E. J. IIiLL 



While botanizing the present season along the Desplaines river 



and some of its tributaries between 



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habits of the cliff-brakes became a subject pf special interest. 



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bordering the flood plain of the river as well as on those by some 

 of the smaller streams which have eroded their beds deep Into the 

 strata as they approach the gorge of the river. Numerous quarries 

 are worked all along the river. The layers of rock are quite hori- 

 zontal, and above the level of the flood-plain run back into the low 

 lulls and are heavily covered with drift. This has been removed 

 in places to some distance back for the purpose of uncovering the 

 stone, but as the ground rises the superincumbent earth becomes 



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 Cliff-like, vertical walls are thereby left similar to those which have 



been made by natural agencies. The wall face thus exposed may 

 have even a greater vertical height than those naturally formed 

 Some have evidently been left untouched by the quarrymen for 

 many years. But no IWara was seen on any of these artificially 

 made exposures, though various mosses and other forms of vege- 

 tation were well established. The fern, wherever found grew 

 upon rocks weathered to a dark gray, and with an exposure doubt- 

 less of many centuries' duration, or dating back to the time when 

 a glacier carved out the rock bed of the river, its face only chang- 

 ing by the slow process of disintegration. In one locality the 

 evidence was particularly strong. An island of rock had been left 

 in the midst of the valley by the passage of the glacier around on 

 either side, and on the old gray rock at the top of the ridge the 

 fern was growing In plenty, but had not wandered down to a subse- 

 quentl)' exposed rock-face made by quarr3-ing below. This is not 

 because the rock recently uncovered docs not furnish cavities or 

 shelves on which plants can readily grow, for the layers are rela- 

 tively thin usually, from the thickness of flagstones to dimension 

 stone two or three feet In depth, and crevices occur plentifully 



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