170 Conidial Stage of Sclerotinia Mespili Schell. 



produced on a leaf in the open were measured and found to be from 

 12 x 10-5/x to 25 x 20-5/x (mostly 18-22 x 16-20/a), with an average 

 (of 100 conidia) of 19-3 x 17-1/x; these dimensions are in close conformity 

 with those given by Schellenberg which are 15-18-20 /x. 



The disjunctors were from 3-1 1/x, or more, in length (usually 6-9 /x); 

 one conidium was attached to its neighbours by disjunctors 14 and 15 /x 

 long respectively, and one disjunctor as long as 17/x was observed, but 

 such instances were exceptional. Schellenberg writes, "Der Disjunktor 

 zwischen den einzelnen Sporen wird kraftig ausgebildet und misst 

 1-5-2 /x"; his illustration of a conidial chain however shows disjunctors 

 3-5-5 /x in length. 



Some of the mummified fruits (or rather flowers, since they had 

 remained practically undeveloped) were collected from the trees and 

 examined microscopically; mycelium was found within the tissues, and 

 agar cultures obtained from such mycelium resembled those produced 

 from conidia. Particles of the superficial layers of these mummified 

 flowers, when teased out in water, yielded numerous minute (about 

 3/x in diameter), spherical, spore-like bodies which are probably the 

 ''microconidia" described by Schellenberg. Similar microconidia or 

 "sporidia" are produced by the fungus in agar cultures. In size and 

 mode of development they resemble the microconidia produced by 

 Sclerotinia cinerea and S. fructigena when these are cultivated under 

 laboratory conditions, and also in the fact that they are not known to 

 germinate. 



The macroconidia however germinated readily in distilled water and 

 germ tubes about 20 /x long were produced within four hours, some of 

 the germinating conidia being still attached to one another by the 

 disjunctors (Text-fig. 2). They also germinated on prune juice agar and on 

 agar prepared with a decoction of medlar leaves, but growth was very 

 slow as compared with that of Sclerotinia fructigena or S. cinerea when 

 growing on agar culture media. These cultures of S. Mespili produced 

 pustules of microconidia but no macroconidia. On agar containing an 

 extract of medlar leaves the cultures were dark brown and the browning 

 extended into the culture medium in advance of the hyphae. 



The apparent strict specialisation of the fungus is a feature of practical 

 interest. Two of the outbreaks occurred on medlar trees growing in cherry 

 orchards and the owners were desirous to know whether the medlar 

 leaves were likely to prove a source of infection for the cherries. Sclero- 

 tinia Mespili is not known to attack cherry trees, but there is no experi- 

 mental evidence to show that it is unable to do so. In this connection 



