1022 
Journal of Agricultural Research 
Vol. XXIV, No. la 
found in which penetration of the cuticle had occurred with no apparent 
reduction of pigment. However, before the hyphae had developed to any 
great extent there was evidence of pigment reduction, which proceeded 
quite rapidly. From the evidence so far obtained it appears that the 
pigment was destroyed while the mycelium was developing in the outer 
wall and before actual penetration of the cell occurred. If this be true, 
the hyphae do not actually come into contact with the pigment as such; 
hence even if the latter were toxic, it might have no effect upon the 
fungus. The destruction of the pigment is due either to a substance 
secreted by the hyphae and capable of diffusing in advance of them or to 
independent chemical changes in the host cell brought about by the dis¬ 
turbances resulting from fungus invasion of the outer wall. 
Of interest in this connection is the common observation made during 
these experiments—namely, as the lesion developed on the succulent 
red scales, pigment of normal intensity appeared in the lumina of several 
layers of the uninvaded parenchyma cells below and around the lesion. 
In normal, healthy scales these cells never contain pigment, the latter 
being confined to the cells of the outer epidermis. The significance of 
the appearance of pigment under these adverse conditions can not be 
entirely explained, but it seems to show very conclusively that the 
fungus infection at a given point on the scale not only affects the invaded 
cells but also influences either directly or indirectly the metabolism of 
uninvaded cells for some distance around the lesion. The stimulation of 
anthocyan production by fungus invasion is a matter of common observa¬ 
tion in nature (25). 
varietai, suscejptibiuty of onion sffdungs 
The writer has reported {24) experiments in which Colletotrichum 
circinans caused a damping off of \^ite Globe seedlings under green¬ 
house conditions. It was of interest to note whether young seedlings 
of colored varieties would show any signs of resistance, especially since 
no pigment would have developed at this early stage. Sterilized green¬ 
house soil was inoculated with a pure culture of the organism, and seeds 
of a few of the varieties listed above were planted. The percentage of 
diseased plants in the white varieties were: White Portugal, 85 per cent; 
Giant White Italian Tripoli, 98 per cent; and Queen, 93 per cent; in the 
yellow varieties: Michigan Yellow Globe, 100 per cent; and Southport 
Yellow Globe, 93 per cent; and in the red varieties: Extra Early Red, 81 
per cent; and Southport Red Globe, 95 per cent. The essentially equal 
susceptibility at this stage of all varieties tried, colored and white alike, 
is self-evident.® 
The experimental and observational evidence conclusively shows that 
we have in colored onions a high degree of resistance to smudge but that 
this character is not present or at least not effective in the young seedlings. 
As will be shown later, the active resistant principle is a water soluble 
substance in the dry outer colored scales. This resistance is not to be 
construed as a case of absolute immunity nor is it unaffected by 
environmental conditions. This idea is substantiated by the fact that 
6 Under field conditions in our Northern States, the young onion seedlings, being spring-sown, are ordi¬ 
narily growing in a soil too cool for the development of smudge. This probably accounts for the total lack 
of any report in America of damping off in the field due to the smudge fungus. In England (1922), how¬ 
ever, this organism was foxmd causing a damping off of young seedlings sown in August, at a time when 
soil temperatures were more favorable. This observation was on White Uisbon variety; no seedlings of 
colored varieties were available for comparison. 
