998 
Journal of Agricultural Research ' 
Vol. V, No. 2i 
CAUSE OF SOILSTAIN, OR SCURF 
Halsted (3) was first to attribute the cause of soilstain (scurf) to a 
fungus, Monilochaetes infuscans E. and H. However, Halsted and the 
later writers have left no record of having experimentally proved the 
pathogenicity of the fungus. The writer has found no records of its 
having been grown in pure cultures. Several efforts by the writer to 
obtain the organism from badly stained roots which were kept in storage 
at first yielded negative results. Each time the causative fungus was 
overrun by a varied and rapidly growing flora. Pure cultures of the 
fungus were finally obtained from plantings of young minute spots. Of 
300 such spots, 10 per cent yielded colonies of the causative organism, 
and these were few in number. The plates were examined every day 
and it was found that the fungus did not appear until nearly three weeks 
after culturing. Because of this slow growth, the fungus in previous 
work was overrun by secondary invaders. The cultural work empha¬ 
sized the necessity of making a large number of poured plates when 
working with an apparently difficult organism. The first reference to 
the fact that this fungus had been grown in culture was made by the 
writer (8, 9) in 1914 and also recently by Harter (4). Using pure cultures 
of the fungus, the writer reproduced the disease several times at will. 
MORPHOLOGY AND PHYSIOLOGY OF THE FUNGUS 
It has been stated that Halsted first named the organism. Although 
some figures are recorded in Halsted’s bulletin (3), yet they are only 
fragmentary and do not take account of all the various stages of the 
morphology of the fungus. Halsted’s observations of the fungus must 
have been limited to material on the host. In pure culture the fungus 
grows very slowly. It is characterized by small darkish round colonies 
(PI. LXXVI, fig. 1) varying from one-tenth to one-fifth of an inch in diam¬ 
eter. The growth is fioccose at the top, and anastomosed below, having 
a resemblance to a stroma in the substratum of the medium. The surface 
growth of a colony resembles that of species of Altemaria and some 
species of Cladosporium, but differing from these by its restricted slow 
growth. The surface of the colony of M. infuscans has an ashen color, 
which is also the general appearance of the fruiting. The fungus grows 
better on vegetable plugs and is at its best on steamed onion and celery 
stalks. The aerial mycelium is branched, septate, and hyaline when 
young (PI. EXXVII, n, w). With age the mycelial cells turn gray, then 
black, and become filled with oil globules (PI. LXXVII, /, r). The sub¬ 
merged hyphae are made up of smaller cells which in old cultures swell 
and take on the appearance of chlamydospores. The conidiophores 
are distinct from the mycelium (PI. LXXVII, a), and not obsolete, as 
stated by Stevens (7). From extended observations it was found that 
conidiophores do not arise in clusters, but are always formed singly 
