438 



.TOUKNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



" We first noticed the fungus on E. japonicus two years ago on a bed of 

 young plants we had bought in for planting out for stock, and which we 

 dug up and burnt. We believe the fungus appears principally on 

 imported plants, as plants of our own raising are quite free from it." 



The distribution of the fungus suggests either that the disease has 

 been introduced on the South Coast by the planting of infected shrubs, 

 and that the disease is now spreading inland, or that for some reason 

 plants of E. japonicus growing near the sea are more susceptible to the 

 disease than those growing inland. 



A peculiarity of the present mildew is the capacity it possesses of 

 persisting by means of hibernation of its mycelium. If the leaves of 

 affected shrubs are examined in the winter months, many will be found on 

 which the mycelium persists in the form of definite rounded or irregular 

 patches. These patches of mycelium have an almost crustaceous con- 

 sistency, and are completely barren. During the winter months these 

 patches of persistent mycelium often become cracked, or even partially 

 disintegrated in places, with the result that here and there the companent 

 hyphns become indistinguishable. If leaves bearing these hibernating 

 mycelial patches are placed in a damp atmosphere (e.g. on wet blotting- 

 paper in a closed glass dish) in a greenhouse at a temperature of about 

 65° F., the fungus at once begins to renew its growth, and after a few 

 days produces conidiophores and conidia. In nature the mildew appears 

 able, by means of this compact hibernating mycelium, to exist continuously 

 on the evergreen leaves of E. japonicus, the mycelial hyphre remaining 

 dormant through the unfavourable winter months, and (possibly through 

 the stimulus of increased nutriment supplied by the haustoria at the 

 supervention of favourable conditions) again producing conidia to infect 

 the younger leaves in the spring. A vegetative hibernation effected by 

 certain of the mycelial hyphfe has lately been recorded by Appel (4) in 

 the case of the conidial stage — the well-known Oidium Tuckeri — of the 

 Vine-mildew. 



In the case of most mildews the formation of conidia ceases at the 

 approach of winter, and the production of perithecia, containing ascos]>orcs, 

 takes place (see 6). At this stage the vegetative mycelium dies, but the 

 ascospores serve as resting- spores which carry the fungus through the 

 period when deciduous plants are bare of leaves. In the case of the 

 Euonipmis-mil&ew the fungus seems to have taken advantage of the 

 presence of evergreen leaves of its host-plant to try to produce conidia all 

 the year round, for neither on the Continent nor in England has any pro- 

 duction of perithecia been found to take place. 



Experiments were carried out (see 7) to ascertain the susceptibility or 

 immunity of various garden varieties of E. japonicus, as well as of other 

 species of the genus. In these experiments the following varieties of 

 E. japonicus were found to be fully susceptible : 'aureus,' 1 albo-margi- 

 natus,' 1 ovatus aureus,'' ' micro phyllus, y and \ President Gunter.' E. radi- 

 cans, and its vars. ' microphallus 1 and ' Silver Gem,' proved also to be 

 fully susceptible to the fungus, but the var. ' Carridrei ' was found, as far 

 as the experiments went, to be completely immune. E. nanus proved to 

 bo practically immune when uninjured leaves were inoculated; when, 

 however, conidia were sown on leaves which had been injured by a cut 



