Hill: The Habitats of the Pellaeas 



597 



alono- the planes of joining. Besides the diff-brakc requires only 

 a sli-ht depression on which to grow. Tiny bunches of young 

 plant's and fronds fruiting when less than an inch high, may be 

 detected on the rocks. The plants wedge their roots into crevices 

 so narrow that it is often difficult to get the bunch out intact. It 

 is not easy to account for this preference of the fern for the old 

 weathered surface. There is noticeable, however, a marked differ- 

 ence in the color of the recently exposed stone and that long sub- 

 iectcd to weathering. Some chemical change is produced by at- 

 mospheric agencies, for the freshly exposed surfaces^ ---^ =';- 

 stained with yellow or drab due to the presence of iron-oxide. 

 This color is not seen on surfaces long exposed,. The absence of 

 the Pc//aca may not be due to the presence of certain metallic in- 

 gredients in excess, but they suggest a possible or partial 

 lu.. of it I am able to state in addition that similar condi- 

 tions have also existed in other localities where I have collected 

 this fern, as witnessed by data on the herbarium labels. These 

 were limestone cliffs in Kankakee county. III, they being formed 

 the same Niagara limestone as that along the Desplaines, 



are soon 



cause 



the lower magnesian limestones along Root River, Preston, Minn., 



Mendota. Madison, Wis. I have 



seen the fern in other places, but no memoranda of its habitat be- 

 ino- made at the time, I cannot speak with accuracy, but am im- 

 pressed with the recollection that the exposures were very old- 

 Most authorities that mention the kind of rock on which the cliff- 

 breik -rows give limestone, but sandstone or other habitats are 



also mentioned. 



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aversion to shade. In the localities along the Desplaines it is 

 mostly found in quite bright sunlight and on rock faces exposed 

 in such a way as to be not only dry but very warm. Wherever 

 the ledges were shaded but a little by trees the Pd/aea ceased to 

 ^.... Some streams entering the river were examined. One had 

 cut a deep gorge in the limestone below Lockport, and there were 

 numerous exposures of the gray-weathered stone. But the fern 

 was only seen in one place where a sharp bend in the stream, with 

 the comparative absence of trees to shade it, gave the cliff a lull 

 exposure to the south. Another stream had made its way down 



grow. 



