Isolates representing nine genera and 28 species were cultured on eight natural substrates and two media. The object was to compare the effect of natural substrates on the morphology of characters currently employed to delimit genera and species of this group of fungi. Observations clearly show that valid distinctions cannot be made among most of these fungi on the basis of characters such as relationship of pycnidia to substrate, rostrate or nonrostrate pycnidia, pycnidial hairs or setae, presence or absence of stromata and distribution of pycnidia, single vs. multiloculate stromata, and paraphysis. It is proposed that pycnidiospore characters, such as gross morphology, ornamentation, and size, would be more useful for distinguishing genera and species than are those characters now employed.