46 
Journal of Agricultural Research 
Vol. XXIII, No i 
on the potato. Observations made at various stages in the process 
showed that the mycelium enveloped but did not penetrate the blocks. 
The middle lamellae first softened, then the cell contents and cellulose 
walls. The starch grains were corroded and eventually entirely dis¬ 
solved. If the mycelial mass surrounding the space originally occupied 
by an individual block was broken open at the proper stage it was found 
to inclose a cavity approximately the size and shape of the original 
block but containing nothing but a residue of liquid. Earlier stages 
showed free starch granules or disintegrating tissue. The starch appears 
to be the last of the solids to disappear. If the cultures were allowed 
to remain undisturbed for a sufficient period, at least partial autolysis 
of the mycelium and sclerotia occurred and the flasks instead of being 
practically filled contained a more or less compact aggregate of mycelial 
slime and embedded sclerotia of 200 or 300 cc. volume nearly submerged 
in a few hundred cubic centimeters of brown liquid. 
Examination of the raw potato blocks at various stages of disinte¬ 
gration indicated that the fungus accomplishes its work without pene¬ 
trating the tissue. The logical inference is that digestive enzyms are 
secreted which dissolve the host tissue and the digested material becomes 
available to the fungus by diffusion and osmosis. Taubenhaus 5 made 
no special study of the enzymic activity of the fungus but states that— 
infection seems to be favored by an emzym secreted by the advancing mycelial 
strands. . . . Fungous hyphae are not found within the cells but only between 
them where the middle lamella has disappeared. 
Under the artificial conditions of the writers' flask experiments even such 
mycelial penetration appeared confined to a very shallow surface layer 
or failed entirely. 
Enzym preparations of the hyphae obtained by the acetone-ether 
method and enzym-bearing powders obtained from the amber liquid by 
the alcohol precipitation method were used in studying the action of the 
fungus. Disks of raw potato in water were treated under aseptic con¬ 
ditions with each of the enzym preparations as well as with filtered water 
extracts of each of them. Such disks invariably softened to the con¬ 
sistency of curd, whereas control disks similarly handled but with the 
addition of no enzym-carrying preparation or extract remained firm. 
Similar results were obtained when toluene was used as an antiseptic 
without special precautions against the entrance of organisms. The 
disks disintegrated through the softening of the middle lamellae and the 
consequent freeing of the individual cells, just as may be seen in the 
initial stages of decomposition in the presence of the fungus itself. 
SUMMARY 
(1) Infection of the Irish potato plant with Sclerotium rolfsii Sacc. 
may manifest itself in a variety of symptoms which, according to their 
appearance, may be grouped as seed-piece rot, damping-off, stemrot, 
wilt, and blight. 
(2) Infection of the potato tuber results in a progressive soft white 
rot) which may take on a so-called “ melter ” form with profuse extrusion 
of liquid. 
(3) The destruction of the host tissues may be accomplished without 
hyphal penetration by means of digestive enzyms. 
(4) Existence of varietal strains in the fungus known as Sclerotium 
rolfsii is quire apparent from the physiological and morphological dif¬ 
ferences of the cultures studied by the writers. 
6 TAUBENHAUS, J. J., OP. CIT., p. 132-133. 
