178 
Pathologie 
BAYLISS, JESSIE S., Observations on Marasmius oreades and 
Clitocybe gigantea, as parasitic fungi. (Journ. Econ. Biology, 
1911, 6, 111 —132, 7 fig. in text and 3 plates.) 
Marasmius oreades , a common „fairy ring“ fungus, is parasitic on 
grasses. The roots of the infected plants have a tendency to branch more 
than those of the uninfected ones and their root tips are frequently stunted. 
The fungus penetrates, and entirely consumes the soft parenchymatous 
parts of the roots and leaves untouched the tough axial stele. The fun¬ 
gus finally enters the grass leaves but not until they are almost dead. 
Experiments showed that an active peptonizing enzyme (peptase), which 
digests vegetable fibrin, and also a peptolytic enzyme (ereptase) which 
digests Witte petone, were produced by the fungus. These enzymes are 
no doubt the cause of the stimulating action of the fungus when it first 
attacks the grass plants, since by means of them it breaks up organic 
compounds of the soil which would otherwise be unavailable for the grass. 
The amount of mycelium at first is not excessive, so that its destructive 
influence is more than compensated for by the extra supply of nitrogenous 
food material it renders available for the grass plant. This stimulating 
effect of the fungus on the grass shows above ground in the darker 
colouration and improved growth of the grass just outside as well as 
inside the dead grass zone. Evidence seems to show that the grass, if 
vigorous, will resist infection by the fungus and offers some explanation 
of „fairy rings“ only appearing on poor pastures. Infected soil is very 
impervious to moisture owing to air entangled within the meshes of the 
mycelium. The fungus secretes some substance toxic to itself and so is 
not able to grow in the same soil three years in succession; during the 
second year the fungus dies off and the grass gains the upper hand and 
flourishes owing to the increased nitrogenous food available; hence, the 
„fairy ring“ of rich luxuriant grass within the dead grass zone. The 
secretion of this toxic substance accounts for the disappearance of rings 
between the places of intersection when „fairy rings“ meet. „Fairy rings“ 
formed by Clitocybe gigantea agree in general with those formed by 
Marasmius oreades. J. Ramsbottom (London). 
DALE, Elizabeth, On the cause of ,Blindness 4 in Potato tubers. 
(Ann. of Bot, 1912, 24, 129—131.) 
The author summarises her results as follows: „The mycelium of 
Verticillium albo-atrum is present in ,blind 4 potato tubers, where it causes 
the destruction of most of the ,eyes 4 . It grows up into the new shoots, 
when any are formed, and in some cases it may pass into the subaerial 
shoots. In other cases it never goes beyond the subterranean stems and 
creeps along them into the newly-formed tubers, internally as a colourless 
mycelium in the cortical tissues, and externally as a scanty thin brown 
mycelium. Thus the tubers may be infected by means of the vegetative 
mycelium only, without the formation of any kind of spore. The course 
of the fungus from the old to the new tuber may be traced by means of 
the brown colouration of the affected tissues. Tubers have been grown 
in three successive years from the original diseased crop, and in each 
year some have been blind and have had a warty and corky outer surface.“ 
J. Ramsbottom (London). 
