TAXONOMIC CHARACTERS OF ALTERNARIA AND MACROSPORIUM 465 
general lack of luxuriance, lack of color in submerged mycelium and 
absence of aerial mycelium. This reached the extreme on the leached 
agar, where the aerial mycelium was almost entirely lacking and the 
submerged mycelium colorless and not at all characteristic, with the 
exception of M. sarcinaeforme . 
The comparative studies noted above were made with cultures 
which were ten days old, but all of the cultures were maintained thirty 
days or longer — sometimes ninety days. In some cases marked 
variations due to age were noted in the spores. In several species 
secondary growth or development of spores occurred which entirely 
destroyed their distinctive characters. This secondary development 
consisted in a multiplication in the number as well as a great enlarge- 
ment of the cells. This caused the spores to become very irregular in 
form, much darker, deeply constricted, and very much larger than 
normal (Plate XIX: 2, 6, 10). 
As a result of the secondary development, the spores of Alternaria 
assumed the form of Mystrosporium, as was pointed out by Constan- 
tin (4). Corda (6) in his description of the genus Mystrosporium 
made figures which are undoubtedly of Alternaria spores in an advanced 
stage of secondary growth. Later (6) he figured the development of 
M. stemphylium Corda from the regular form of a young Alternaria 
spore through the various stages of secondary development to the 
very irregular form called Mystrosporium. From the descriptions of 
species of Mystrosporium there is no doubt that most if not all of them 
belong to Alternaria. All specimens labeled Mystrosporium which I 
examined in the exsiccati were Alternaria in various stages of secondary 
enlargement. 
Young colonies of all species of Alternaria produced smooth regular 
spores which remained regular for a time interval which varied in 
different species and on different media. The richer the medium the 
earlier the secondary enlargement began. The first indications of 
this secondary growth were multiplication of and deep constriction at 
the septa. On leached agar no secondary enlargement occurred in 
any species, even after a lapse of three or four months. There occurred 
irregularly in all species a well-marked echinulation of the spores. 
Beyond a deep constriction at the septa, no secondary change was 
noted in Macrosporium, nor in A. sonchi, A. brassicae var. microspora, 
and A. solani from potato. This last, however, produced spores in 
numbers sufficient for observation only on leached agar where secon- 
dary enlargement did not occur in any species. 
