190 On Diseases of Plum Trees 



hours, by swelling along the short diameter, are converted into spheres, 

 from which eight to ten hours later 1-4 germ tubes protrude (cf . Fig. 8). 



The isolation in pure culture of members of this genus is rendered 

 easy by the production of tendrils of spores. A small piece of tendril 

 is placed in a drop of sterile water, and spores transferred from this to 

 the required medium. When large numbers of cultures were required 

 it was found most convenient to make stock cultures on grape-gelatine, 

 from which mycelial inoculations were carried out. 



In nearly all cases, mycelial growth followed by pycnidial formation 

 takes place with great rapidity. 



There is an entire absence of any definite stroma, or limiting layer ; 

 the pycnidia being developed on small cushions of hyphae (cf. Fig. 9) 



Fig. 9. Fig. 10. 



and the hyphae of the general tissue passing gradually into conidio- 

 phores. 



On cutting sections of a very young pustule (it is best to take one 

 growing on agar material), it is seen to be a solid mass of interwoven 

 hyphae. As growth continues, spaces appear, which later become 

 chambers. These chambers are lined with sparingly-branched coni- 

 diophores, which are full of minute darkly staining granules, specially 

 noticeable as the conidiophore walls stain only feebly. Later, conidia 

 are abstricted from the tips of the conidiophores. One or more pores 

 now appear in the pycnidia, through Which drops of water are extruded, 

 followed by the spores, either as pink tendrils, or more often, owing to 

 the saturated atmosphere, as pink droplets. 



The media employed included grape juice, raisin extract, plum 

 wood extract, alone or stiffened with agar or gelatine; artificial nutrient 

 solutions; and solids, e.g. potato, carrot, turnip, and plum wood. 



