126 The Irish Naturalist. 



P. undulatus may be known from P. pcrfoliatus by its com- 

 pressed stem ; this is easily seen when the plant is fresh, but 

 is lost when dried ; also by its leaves only half clasping the 

 stem (not wholly, and cordate, as in pcrfoliatus). Usually the 

 nerves are much fewer than in pcrfoliatus ; the early growth 

 is also much like crispus in facies ; but as in all hybrids, it 

 varies much, sometimes inclining to one supposed parent, 

 sometimes to the other. From P. crispzis it may be known by 

 the nearly entire leaves (the apex of which has minute per- 

 sistent spines) not serrated as in crispus. Usually the mature 

 upper leaves are much broader than generally is the case in 

 crispus ; but I have seen a specimen of true crispus with leaves 

 nearly as broad as some of the undulatus forms. 



AMERICAN BIRD-VISITORS TO IRELAND. 



BY W. E- PRAEGER, KEOKUK, IOWA. 



VII. — The White Jer- Falcon {Falco islandus, A.O.U. Check- 

 list ; F. candicans, most authors). 

 A glance over what has been written on the Jer- Falcon in 

 our systematic works, will convince the reader that in orni- 

 thology also the old saying is true, " Doctors differ." No two 

 authorities are quite agreed as to how many species of the 

 great falcon of the Arctic regions ought to be recognised. 

 The Jer-Falcous from various countries differ greatly from 

 each other, yet for the most part they intergrade perfectly ; 

 and the discussions of the savants, after all, only prove that 

 such things as .species do not reall}- exist in nature, but are 

 artificial groups, adopted for our own convenience, or in 

 deference to the opinion of our predecessors. 



The Jer- Falcons inhabit the Arctic and Sub-Arctic regions. 

 They are true Falcons, [possessing the pointed wing and 

 toothed bill of this genus, of which they are the largest repre- 

 sentatives. A length of from 20 to 24 inches distinguishes 

 them from all their smaller allies. As is often the case in 

 Arctic birds, the tarsus is more extensively feathered than 

 among the more southerly species of the same genus. There 

 should be no trouble telling a Jer-Falcon at sight irrespective 

 of its colour ; but when we come to that characteristic, on 

 which the various species or sub-species are based, the ques- 

 tion becomes very complicated, and need not be entered on in 

 any detail here. It will be sufficient to say that in Labrador 



