BORDER SPECIES. 



ESIDES the truly representative spe- 

 cies of eastern America, there are 

 a few whose centre of distribution 

 is beyond our limits but which 

 stray far enough over the borders 

 to make some mention of them 

 desirable. 



The Rock Brake. 



One of the most interesting of the border species is 

 the rock brake (Cryptogramma acrostichoides) which 

 inhabits the far North. In the East it reaches to 

 Labrador and the country north of Lakes Huron and 

 Superior, but in the West it is found in Colorado and 

 California and extends from thence to the Arctic Circle. 

 It is an inhabitant of rocky places, growing in the chinks 

 between the stones, often in dense patches. 



The plants are usually from six to eight inches high. 

 The stipes of the fertile fronds are about twice as long 

 as those of the sterile, so that there are usually two 

 tiers of fronds. Both are ovate-oblong in shape, the 

 sterile rather thin and twice pinnate with ovate pinnae 

 and toothed or lobed rounded pinnules, while the fertile 

 are three times pinnate, with long, narrow, podlike pin- 

 nules, due to the edges being rolled back to the midrib. 

 The sporangia are borne in roundish sori near the mar- 

 gins which are slightly altered to form the indusium. 



