H. WORMALD 33 



contaminated were transferred to other plates. When each had reached 

 a sufficient size sub-cultures were made as required. 



(2) AMien the fungus was found as barren mycelium only, as it 

 occurs within the tissues of the newly infected twigs, transverse sections 

 were made through the lower portions of the affected parts, i.e. either 

 across the node itself where infection had arisen or through the diseased 

 tissues of the internode below^. Particles of the sections were teased out 

 in sterile distilled water and placed on agar plates. The mycelium present 

 in the sections usually grew out uncontaminated by other forms so far 

 as could be seen, but to ensure absolute purity of cultures sub-inocula- 

 tions were made from the outgrowths by placing peripheral portions of 

 the resulting mycelium on sterilized potato, a medium which has hitherto 

 proved "the most favourable for conidia development, and when the 

 conidia were being freely produced some of them were isolated on plates 

 and pure sporelings obtained as described under (1). 



Agar-agar, containing an extract of prunes, either as plates or as 

 *' slants" in test tubes, was used for studying the mode of growth, and 

 sterilized potato in wide test tubes or in Roux's tubes was used when 

 conidia were required for measuring or for inoculation experiments. 



When placed on the nutrient agar the mycelium grows out readily, 

 producing within a few days a regular, almost circular disc of hyphae; 

 later the margin develops into broad lobes with narrow sinuses between 

 them. As in the case of the Apple Blossom- Wilt strains, growth is 

 usually arrested at about 2 cm. from the centre but is resumed as 

 flabelliform outgrowths which generally originate at the sinuses. 



It has been shown that the form of Monilia cinerea infecting the 

 apple flower, as represented by some thirty strains from various sources, 

 invariably produces a brown coloration when growing on agar-agar con- 

 taining an extract of prunes. The eleven strains obtained from plum 

 twigs have shown some variation in the intensity of this coloration. One 

 has remained quite colourless in most of the plate cultures of the medium 

 and colourless or almost so as slant cultures in test tubes; one has pro- 

 duced a coloration indistinguishable in intensity from that of the apple 

 blossom strains, while' the others are intermediate. 



When growing on sterilized potato in test tubes or in Roux's tubes 

 all the "Wither Tip" strains tested have produced a copious supply of 

 conidia, numerous grey tufts of conidiophores, usually in more or less 



1 The terminal internodes, which wither because the transpiration current is interrupted 

 by the death of the tissues actually invaded by the fungus, do not themselves necessarily 

 contain mycelium. 



Ann. Biol, v 3 



