TRANSACTIONS OF SECTION K. 821 
9, Further Cultural Experiments with ‘ Biologic Forms’ of the 
Erysiphacee. By Ernest 8. Satmon, £.L.S. 
In a recent paper! the author described a method of culture by means of 
which the conidia of ‘biologic forms’ of Erysiphe Graminis, DC., can be induced 
to infect leaves of host-species which normally are immune to their attacks. In 
this method of culture the vitality of the inoculated leaf was affected by cutting 
oS piece of its tissue, or by injuring the leaf by touching it with a red-hot 
nife. 
In the present paper further methods are described by which the same result 
can be obtained. 
A preliminary series of experiments proved that the ascospores of a ‘ biologic 
form’ are able, in the same manner as the conidia, to infect leaves injured by the 
removal of a piece of the leaf-tissue, although quite unable to cause any infection 
of the uninjured leaf of the species used. 
An extensive series of experiments was then made in which the leaf previous 
to inoculation had been injured in one of the following ways: By pricking with 
a pin, by stamping out a circular piece of the leaf with a cork-borer, by allowing 
slugs to eat away portions of the leaf, by pressure with weights, or by nipping 
the leaf with a pair of forceps, 
Leaves injured by the action of narcotics and heat were also used, the leaf 
previous to inoculation being exposed to ether, chloroform, or alcohol vapour, or 
immersed in a mixture of alcohol and water, or heated gradually in water to 
49°:5 or 50° C. 
The results of the experiments carried out prove that not only mechanical 
injuries, such as wounds from cuts, bruises, attacks of slugs, &e., but also injuries 
due to the action of narcotics and heat, cause a leaf to become susceptible to a 
‘biologic form’ of a fungus to which it is normally immune. 
Attention is directed to the fact that these cases of the loss of immunity 
brought about by causes which affect the vitality of the leaf find their exact 
parallel in the recorded instances of induced susceptibility in animals to certain 
diseases caused by bacilli. 
To describe cases where a form of a fungus which is specialised to certain 
host-plants and confined to them under normal circumstances proves able to 
infect injured parts of a strange host the author proposes the terms wvenoparasite 
and wenoparasitism. The terms may be used also in the cases where fungi which 
live usually as saprophytes prove able to infect injured parts of living plants. In 
the case of the specialised fungus, when on its proper host, the terms @coparasite 
and. ecoparasitism are proposed. 
A series of experiments was carried out with the object of ascertaining the 
infection-powers of the conidia of the first generation produced on barley-leaves 
inoculated—after having been rendered susceptible by the action of ether, or 
alcohol, or heat—with conidia taken from wheat. In the sixteen cases the conidia 
produced on such treated barley-leaves proved, when sown simultaneously on 
normal leaves of barley and wheat, totally unable to cause any infection on the 
barley, while causing in every case full, and usually virulent, infection on the 
wheat. In order to see if any subsequent variation would occur in the infection- 
powers of the conidia of the fungus produced on the treated barley-leaves, conidia 
of the successive generations produced on wheat, up to the sixteenth generation, 
were cultivated. In every case the conidia proved able to infect fully leaves of 
wheat, while never producing any sign of infection on barley. 
These experiments demonstrate the fact that the infection-powers of a ‘ biologic 
form’ are not altered by its residence for one generation on a strange host-plant 
treated in the manner described, and give also some evidence in favour of the idea 
of the hereditary nature of the infection-powers of certain ‘ biologic forms.’ 
\ Phil. Trans., vol, exevii. 1904, pp. 107-122. 
