Further Cultural Experiments with ‘Biologic Forms’ 
of the Erysiphaceae \ 
BY 
ERNEST S. SALMON, F.L.S, 
Introductory. 
I N a recent paper (1) I have described certain methods 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 the present paper further methods are de- 
scribed by which the same result can be obtained. A series of experiments 
has also been carried out with the object of ascertaining the infection- 
powers of the conidia of the first generation of the Fungus produced on 
leaves rendered susceptible by certain treatments, as well as the infection- 
powers of the conidia of succeeding generations. In the first part of the 
paper the various methods of culture which have been used will be briefly 
mentioned, as well as the results obtained concerning the infection-powers 
of the conidia. The second part of the paper will describe more in detail 
the experiments carried out. 
Part I . — The methods, which I have previously described, of inducing 
susceptibility in a leaf normally immune to the attacks of the ‘ biologic 
form ’ of the Fungus used, have consisted in affecting the vitality of the leaf 
by cutting out a piece of its tissue or by injuring the leaf by touching it 
with the red-hot point of a knife (see (1), pp. io8, hi). Conidia of 
‘ biologic forms ’ which are unable to infect normal uninjured leaves of 
certain host-species proved able to do so when sown at these injured 
places. 
This method of culture of removing by a cut with a razor a small 
piece of leaf-tissue was again successfully employed in the preliminary 
experiments of the present series (see Part //, sect. a). Further, the results 
of several experiments have demonstrated the fact that the ascospores of 
a ‘ biologic form ’ are able, like the conidia, to infect such injured leaves, 
although they proved, in experiments previously carried out and here again 
repeated, to be unable to infect uninjured leaves of the host-species used. 
1 From the Jodrell Laboratory, Royal Botanic Garden, Kew. Read before the Botanical 
Section of the British Association, Cambridge, August, 1904. 
[Annals of Botany, Vol. XIX. No. LXXIII. January, 1905.] 
