466 
JOHN A. ELLIOTT 
V. DISCUSSION 
A general survey of the characters upon which specific descriptions 
of Alternaria and Macrosporium are, or may be, based is fitting in 
this place. 
Broadly considered, the different bases for descriptions may be 
divided into natural morphology, cultural morphology and media 
changes, and host relations. In the present studies effort was made 
to get a fair estimate of the value of each of these by studying them 
under various conditions. In specific descriptions the shape, size, 
and color of spores are generally given. Also septation, constriction, 
and echinulation are more or less frequently mentioned. In many 
instances one of these characters may furnish the only point of differ- 
entiation of one species from another species in the description of 
which that character is not mentioned. The conidiophores are gener- 
ally more or less definitely described, the characters commonly given 
being, length, width, septation, constriction, color, branching and 
geniculation. As in the case of the spore characters, any one or all of 
these characters may be neglected by one author or made the basis for 
specific description by another. The nature of the submerged my- 
celium has been made the basis for specific descriptions in some cases, 
although in many cases it is not mentioned. In artificial cultures 
where the mycelium is easily studied it is generally taken into con- 
sideration. The characters noted are thickness, length between sep- 
tations, color, constriction, fasciculation and rate of growth. Aerial 
mycelium is not often mentioned in specific descriptions. Length, 
width, color, abundance, and general habit are the characters con- 
sidered. 
Morphology 
I. Spore: The previously described experiments show that, within 
the natural range, the size of the spores under natural conditions was, 
in almost all of the species studied, quite constant, although under 
ordinary cultural conditions the size of the spore on artificial media is 
usually less than that on the natural host. However, in a relatively 
short time — two to six weeks — in some species there is a marked 
secondary development. 
The most characteristic thing about the spores of these fungi is 
their shape which is an immediate index to the genera, and generally 
to the species. All obclavate, cuneate, ovate, pointed or beaked spores 
belong to Alternaria and under suitable conditions form chains. There 
