TAXONOMIC CHARACTERS OF ALTERNARIA AND MACROSPORIUM 467 
is variation in shape within a single species, but in most cases under 
natural conditions the shape of the spore, combined with its size, 
identifies the species. Parasites, as they are collected during the 
period of active attack upon plants, are uniform in spore form. Some 
species wintering on decaying leaves showed a secondary development 
which quite destroyed their characteristic form and size and made 
recognition impossible. On artificial media where secondary growth 
occurred frequently, the shape of the spores was greatly changed. 
All Alternaria spores have a more or less acute apex and some species 
have beaks. In some cases the beaks are six or seven times the length 
of the spore itself. This, however, occurs only when they are not 
borne in chains, or in the terminal one of a chain. In the chains the 
terminal spore is formed by budding out of the apex, or occasionally 
from the side, so that the spore above takes the place of the beak of 
the spore below. For this reason the length of beak alone cannot be 
taken as of great value. Many species of Alternaria do not have 
beaked spores, so to a certain extent the beak is a specific character. 
There is marked difference between species in the number of septa. 
Septation is dependent on the size of the spore in a single species, but 
independent of the size of spore in different species. The amount of 
septation increases with the age of the spore. The same conditions 
which brought about changes in shape and size of spores, increased 
the number of septa and constriction at the septa. 
Echinulation occurred at times in all of the species studied. In 
some cases part of the spores from a colony were echinulate while others 
were smooth. 
When the age of the spore is considered, color is an important 
character of some species. Generally spores darken with age. Alter- 
naria dianthi and A. hrassicae var. microspora grown at 10° showed 
marked color change, both being very light amber instead of the 
normal dark olive. A. fasciculata, forming spots on partially etiolated 
cabbage leaves and also in growing on raw disinfected cabbage leaves 
and petioles, showed a similar change. 
2. Conidiophore: The form of the conidiophore is often quite 
characteristic, although length depends upon the age and environment. 
In Macrosporiiim sarcinaeforme the end of the conidiophore becomes 
swollen before the spore appears. If this spore falls off another bud 
forms at the end of the conidiophore, producing another "joint" 
which in turn swells at the end and produces a spore. If the spore 
