July =3. I9I7 Black Rootrot of Apple 167 



roots of one tree and from the margin of a trunk lesion extending about 

 I foot above the surface of the ground on another. X. polymorpha was 

 also obtained from both these sources. An unidentified fungus, probably 

 a basidiomycete, which invests the roots with a conspicuous mat of white 

 mycelium has been cultured from several sources. It has proved slightly, 

 if at all, pathogenic on excised living apple roots in a moist chamber, 

 but its appearance in the field suggests that it may be parasitic in some 

 cases, probably on unthrifty trees. 



Cultures of species of Xylaria were obtained during 19 15 and 191 6 

 from orchards located at 1 1 places in Virginia. Three species are repre- 

 sented. 



Xylaria hypoxylon has been obtained from nine places: Winchester, 

 Middletown, Pleasant Valley, Staunton, Fishersville, Cloverdale, Blacks- 

 burg, Buena Vista, and Greenwood. The isolations from the last two 

 places are tentatively assigned to this species, but differ from the t5^pical 

 X. hypoxylon in certain constant cultural features; whether these are of 

 specific or varietal character remains to be determined. 



Xylaria polymorpha has been obtained from two orchards at Barber. 

 The identity of the cultures obtained from apple roots has been estab- 

 lished by comparison with cultures grown from ascospores taken from 

 mature stromata on apple roots and locust stumps. 



Xylaria sp. from Harrisonburg fe distinct from the two preceeding 

 species. In culture it resembles X. cornu-damae (Schw.) Berk, obtained 

 from germinated ascospores from locust, but its identity with this species 

 is problematical. 



CULTURE FEATURES OF THE XYLARIAS 



All species of Xylaria grew readily on a variety of nutrient media. 

 Gueguen (6), Harder (8), and Freeman (2) have studied the develop- 

 ment of X. hypoxylon in culture, and Gueguen (7) has also described 

 pure cultures of X. polymorpha. Our experience that stromata of X. 

 hypoxylon bearing conidia are produced on a variety of culture media is 

 in agreement with their findings. Freeman, however, states that ascos- 

 pores were produced in cultures of X. hypoxylon on steamed blocks of 

 elm wood in six or eight weeks. We have not succeeded in obtaining 

 ascospores in any of our cultures. 



Czapec agar ^ and a starch-agar medium have been used in most of our 

 isolation and culture work, the former being preferable for the produc- 

 tion of stromata. The colonies of the three species in petri-dish cultures 

 are easily distinguished. Colonies of Xylaria hypoxylon (PI. 16, D) 

 have considerable aerial mycelium with strongly marked, irregularly con- 

 centric zones, irregularly lobed margins, and dark pigmentation. Col- 

 onies of X. polymorpha and Xylaria sp. have appressed mycelium with 



1 Cane sugar, 30.0 gm.; magnesium sulphate, 0.5 gtn. , potasium chlorid, 0.5 gm ; potassium acid phosphate, 

 i.o gin. ; sodium nitrate, 2.0 gm.; irou sulphate, trace; agar, 20.0 gm. ; water, 1,000 c. c. 



