288 



COMPARATIVE MORPHOLOGY OF FUNGI 



or dry fruits (as X. carpophila on beechnuts). From the ascospores 

 develops an extended mycelium whose hyphae unite into thick strands; 

 these grow tall and show an intense heliotropism so that even when under 

 bark or tree trunks they easily come to the outer surface. They are first 

 differentiated into a black pseudoparenchymatic rind and a light fibrous 

 core and then gradually develop to the cylindrical, clavate or branched fruc- 

 tifications. Many species (inconvenient forsystematists!) are inseparable 





' 



Fig. 18S. — Xylaria Hypoxylon. Group of stromata on fallen wood. {After Tulasne. 



from Hypoxylon, thus X. obovata, X. anisopleura and X. allantoidea show 

 in the same species all sorts of transitional forms from Hypoxyloid central 

 attachments to Xylarioid stipes. In spite of its inconspicuous occurrence 

 in nature, its formation in culture is dependent on conditions of nutrition; 

 thus X. Hypoxylon requires asparagin as a nitrogen source in formation of 

 fructifications, while X. arbuscula and X. polymorpha require ammonium 

 nitrate. Similarly darkness, red, yellow or green light favor vegetative 



