Arthur and Kern: Peridermium 427 



& Earle, Econ. Fungi, no. 221); Isle au Haut, Maine, August 

 16, 1899, and August 17, 1900, /. C. Arthur ; North East Har- 

 bor, Maine, no date, H. de Raas/off. 



A very abundant species, especially in the western mountains. 

 It can be distinguished from Per. dccolorans, with which it is often 

 confused, not only by its common habit of forming witches' brooms, 

 but by its much longer aecium and smaller aeciospores. 



18. Peridermium consimile sp. no v. 



0. Pycnia amphigenous, numerous, scattered, conspicuous, 

 punctiform, honey -yellow becoming blackish-brown, subepidermal, 

 globoid or flask-shaped, almost wholly immersed, 110-150/i 

 broad. 



1. Aecia from a limited mycelium, not changing form of leaf, 

 chiefly hypophyllous, in two irregular rows on yellowish spots 

 occupying part or all of a leaf, flattened laterally, 0.5-1.5 mm. long, 

 0.5-0.8 mm. high, dehiscent at apex; peridium colorless, rather 

 delicate, margin becoming lacerate, cells slightly overlapping, 

 inner thickened, verrucose, transversely striate, outer thinner, 

 smooth; aeciospores broadly ellipsoid or globoid, 16-23 by 24- 

 35/1, wall colorless, rather unevenly thick, 1.5-2.5 p, moderately 

 and densely verrucose. 



On Picea Mariana (Mill.) B. S. P. {Abies nigra Desf.), Junius, 

 New York, July, 1905, E. / Durand (type) ; Lily Swamp, Oswego 

 County, New York, August 4, 1891, W. R. Dudley ; Burlington, 

 Vermont, July 30, 1896, A. J. Grout (specimen in herbarium N. 

 Y. Bot. Garden); London, Ontario, Canada, no date,/ Dearucss 

 (specimen in Crypt. Herb. Harvard University) ; Vermilion Lake, 

 Minnesota, July 20, 1886, E. IV. D. Ho/way. 



On Picea rubra (Lamb.)* Link \Pkm rubeus Sarg.), Adirondack 

 Mountains, Aug. 1873, Chas. H. Feck (specimen in herbarium of 

 N. Y. State Museum, Albany, N. Y.). 



This form has been confused with Per. decolorans on the one 

 hand, and Per. eoloradense on the other. From the former it differs 

 in size of spores and thickening of peridial cells, while agreeing 

 in having an annual mycelium ; and from the latter it differs in 

 never forming witches' brooms and in dehiscence of peridia, while 

 agreeing rather closely in size of aecia and spores. It is usually 

 found in swamps. 



