174 Conidial Stage of Sclerotinia Mespili Schett. 



but reference to Continental mycological literature showed that a similar 

 disease and fungus had been recorded for Switzerland and described in an 

 interesting paper by Schellenberg 1 in 1907. He had observed the diseased 

 condition of the leaves in the open in 1 905 and induced the development of 

 the conidial fructifications on diseased leaves which he had collected; in 

 the following year he found the apothecial form, which he named Sclero- 

 tinia Mespili, on mummified medlar fruit and described the mode of in- 

 fection of medlar leaves by the ascospores. Schellenberg remarked on the 

 peculiar odour given off from diseased leaves and stated that it attracts 

 insects which carry the conidia (the " chlamydospores " of Schellenberg) 

 to the medlar flowers and so cause infection of the latter. He attributed 

 the odour to the conidial fructifications ("so zeigen diese Chlamydo- 

 sporenrasen einen ausgesprochenen, starken Duft 2 "), but the present 

 writer found that diseased leaves on which conidia had not yet appeared 

 were decidedly odoriferous, and a more probable explanation of the 

 phenomenon is that it is caused by an enzymic secretion of the fungus 

 acting on one or more organic compounds present in the tissues of the 

 leaves. 



A few days after the specimens were received a visit was paid to the 

 orchard with the object of ascertaining the source of infection, particularly 

 as Schellenberg's work suggested that the spring infection of the leaves 

 is caused by ascospores discharged from apothecia which develop from 

 mummified fruit lying on the ground. The diseased trees were three in 

 number and on each of them about 25 per cent of the flowering shoots 

 were affected, from one to three leaves on each shoot showing the 

 characteristic blotches (Fig. 1); in some cases two distinct spots were 

 found on the same leaf. No conidial fructifications could be found on the 

 leaves on this occasion so that it would appear that the brown areas 

 represented primary infections, and although there must have been some 

 hundreds of such primary infection spots on each tree, the source of 

 infection was riot discovered. Numerous undeveloped mummified fruits 

 had remained on the trees from the previous year, but no conidial 

 fructifications, corresponding to those which later developed on the 

 leaves, could be found on them. Similar mummified fruits were found on 

 the ground, but, although a careful search was made no apothecia were 

 discovered. 



Towards the end of the same month (April), medlar shoots with leaves 



1 Schellenberg, H. C. "Ueber Sclerotinia Mespili und Sclerotinia Ariae," Cent, fiir 

 Bakt. Abt. 2, Bd xvn, 188-202, 1907. 



2 L.c, p. 193. 



