36 A " Wif/H'r Tip " of Plum Trees 



(d) Identity of the Fungus. 



The fructifications found on the dead twigs during winter and spring 

 were those of a Monilia ; the ashy grey colour of these pustules, their size 

 (not usually exceeding 1 mm. in diameter) and the dimensions of the 

 conidia correspond to descriptions of M. cinerea Bon. as given by 

 Aderhold and Ruhland(2) and by Woronin(i2). The size of the conidia 

 obtained from old dead twigs in summer more nearly coincides with the 

 dimensions given by Aderhold and Ruhland for the conidia of M. laxa; 

 strains obtained from such twigs were however indistinguishable in their 

 mode of growth and in the size of their conidia from those strains ob- 

 tained from twigs producing in winter pustules with conidia considerably 

 smaller and comparable with those of M. cinerea as given by the same 

 authors, when the various strains are grown as pure cultures under 

 laboratory conditions. It follows that, in considering the dimensions of 

 the conidia as an aid to the identification of species of Monilia, the con- 

 ditions under which the conidia have developed must be taken into 

 account. 



Although Monilia fructigena occurs frequently on the fruit itself, and 

 in some orchards causes quite as much damage to the ripening and 

 mature plums as Monilia cinerea, and although the former may be found 

 commonly on trees affected with the "Wither Tip" disease, the writer 

 has never found M. fructigena on the dead twigs nor isolated it from 

 infected young shoots; its occurrence appears to be exclusively on the 

 fruit. 



The "Wither Tip" disease of plum trees is therefore to be attributed 

 to Monilia cinerea Bon. The writer at present prefers to retain this, the 

 name given to the conidial stage of the fungus, in preference to Sclerotinia 

 cinerea for reasons already stated in a previous paper (10). 



The "Brown Rot" fungi are known to be responsible for great losses 

 in other parts of the country where the plum is extensively cultivated, 

 particularly in Cambridgeshire, the Evesham and Pershore districts of 

 Worcestershire, and in Devonshire ; not only are the fruit, blossom and 

 twigs attacked, but the larger branches are often killed. Since the 

 "Wither Tip" fungus readily attacks both fruit and blossom of the plum 

 tree and may form cankers (as shown in this paper), it appears probable 

 that the same form is the one chiefly responsible for the attacks in the 

 districts mentioned. In Devonshire a disease which appears to be 

 identical with the "Wither Tip" of plum trees in Kent is reported^ as 



' Vide, The Fniil-growcr, Fruilcrcr, Flortsl and Markxt (idrdcucr, June J5, I'JIO. 



