174 A Blo.ssoni Wilt ainJ Canker of Ajqth' Trees 



conidial stage, conidia are isolated on agar plates ; the resulting spore- 

 lings which are seen to be uncontaminated are transferred to other 

 plates and when sufficient growth has taken place sub-cultures are 

 prepared from these. Cultures for the continued propagation of any- 

 particular strain are made on agar slants in test tubes. Strains have 

 been obtained in this way from dead spurs, cankers and young apples; 

 one was prepared from conidia induced on a dead truss by placing it in 

 a damp chamber, and another from a "mummied" apple. 



When the fungus is in the form of sterile mycelium only, as in the 

 majority of freshly killed spurs and young cankers, the surface of the 

 affected parts is gently rubbed over with cotton wool damped with 

 absolute alcohol^, and transverse sections are made through the diseased 

 tissues with a sterilised razor. These are dropped into a watch-glass 

 containing sterile distilled water and particles of the sections are then 

 removed with flamed needles (avoiding the outer layers of the cortex) 

 to another watch-glass of sterile water, from which they are finally 

 transferred to agar plates. As a rule cultures which were apparently 

 quite pure could be obtained directly in this way; sometimes, par- 

 ticularly in the case of spurs which had been dead for some weeks, 

 bacterial colonies appeared immediately round the section but sub- 

 cultures taken from the peripheral mycelium could be obtained pure. 

 Such cultures were indistinguishable from those obtained from conidia. 



For comparison with these, cultures of the Brown Rot fungi from 

 other sources have also been prepared, e.g. forms growing on various 

 "stone-fruits" (plum, cherry, damson, peach), on apples and on pears. 

 Each of the strains has been started from a single conidium. In those 

 instances where no viable conidia were present this could not be done 

 directly and the cultures were obtained initially from sterile hyphae ; 

 the production of conidia was induced by growing on sterilised potato, 

 and "single-spore" strains were then prepared. 



I have not yet obtained the ascigerous {Sclerotinia) stage of any of 

 these forms, so have been unable to compare them with the descriptions 

 of that stage as found on the Continent and in America. The fungus 

 which appears so generally on ripening apples is however undoubtedly 

 the M. fructigena as described in Woronin's paper (23), from the large 

 size of its pustules (usually 1-5 to 2 mm. in diameter), the colour of the 

 pustules, which is a buff yellow, and the large size of the conidia ; the 

 latter are usually about 20 ;m in length but often exceed that. This 

 species I have obtained from the apple, pear, cherry, plum and peach, 



^ 94 % alcohol has also been used with equally good results. 



