297 



2. Externally colnied lilack. 



a. Stroma scant, coiniiosed of large perithecia which are almost 

 solitary, or mntliu'iit in variously shaped, thiu-crusted patches. 



1. II. effusiom. 



h. Stroma thick nr lliiii. in more or less effused patches 1/2 to 

 1 or 2 cm. loiiu; and wide. (Some very convex forms might 



he mistakenly placed under III.) 8. H. miiltiformr. 



I. Struma globose or suhglobose. 

 A. Externally colored not lilack. 



1. Stroma glol)ose. 



a. Substance of stroma concentrically-zoned, radiate-fibrous, 

 spores S micrnns long or less .9. //. Howelanum. 



b. Substance of stroma homogeneous, spores more than 8 mic- 

 rons long 10. H. coccmcum. 



c. Sulistance of stroma scant, perforate or granular, ostiola 

 white-margined *6. H. perforatum. 



2. Stroma depressed-pulvlnate or rounded, surface dark purple. 



11. II. fllSCIllll. 



li. Externally colored black. 



1. Perithecia annulate-truncate. 



a. Stroma huge, with the small (.5 mm.) perithecia deeply 

 and eveidy sunk in the substance of the stroma so that 

 scarcely more than the disk projects, .giving a rounded, 

 even appearance 12. II. marginatnm. 



b. Stroma of medium size and irregular from the large (2/3-1 

 mm. I. prominent perithecia, many of which project one half 



their l(MiL;tli beyond the surface of the stroma 



13. H. annulatum. 



2. Perithecia not annulate-truncate. 



a. Stroma scant, perithecia large, solitary or confluent in 



small, elongated areas in grooves of the liark 



l.'i. H. sassafras. 



b. Stroma roughly suhglobose, composed of a few loosely- 

 aggregated perithecia (Usually not over 15 or 20 in a 



* U. perforatum is sometimes found with the effused form of stroma, and again 

 with a suhglobose or hemispherical stroma. In order that the student may not be 

 at a loss to know where to place it in case he should have only the one or the 

 other form, the key has been arranged so that this sijecies will run under either the 

 effused or the globose group. 



