ON A FUNGUS DISEASE OF EUONYMUS JAPONICUS LIMN. F. 435 



over its surface many hundreds of densely clustered conidiophores, and 

 the whole patch becomes powdery with the accumulated ripe conidia. An 

 enormous number of conidia are produced : these are blown about by the 

 wind, and quickly spread the disease. In damp shaded places, protected 

 from the wind, the leaves of affected shrubs soon become coated with a 

 dense floury mass of conidia, so that a thick clinging scale-like covering, 

 or incrustation, is found over the greater part of the leaf. If the boughs 

 of such plants are shaken, a shower of white dust-like conidia falls to the 

 ground. 



After a short time the separate patches of mycelium, which occur on 

 both surfaces of the leaf, increase in size and become confluent. The 

 affected leaves soon afterwards turn yellowish in the neighbourhood of 

 the fungus, and, unless the disease is checked, they begin to fade and are 

 prematurely thrown off. Instances often occur in which leaves bearing 

 patches of the mycelium on the lower surface show groups of cells on the 

 upper surface (exactly opposite the patches of mycelium) which have 

 changed their colour, and appear as pale yellowish blotches on the dark 

 green upper surface of the leaves. Besides the injury caused to the 

 leaves, the fungus, in severe outbreaks of the disease, invades the young 

 wood of the twigs, covering them for an inch or more with a continuous 

 patch of conidia-bearing mycelium. In such cases the normal growth of 

 the shrub is seriously interfered with. 



Some experiments which I have recently carried out (7) have shown 

 the high degree of susceptibility of the leaves of E. japonicus to the 

 attacks of the present fungus, and the rapidity with which the fungus 

 can spread from leaf to leaf. Leaves were inoculated by placing conidia 

 on the epidermis, and then kept in a damp atmosphere. By the third day 

 it became evident that infection had taken place, fine branched hyphie, 

 which radiated in all directions from the sown conidia, being now visible. 

 By the fifth or sixth day the production of vigorous patches of mycelium, 

 2-3 mm. across, and bearing many hundreds of nearly ripe conidio- 

 phores, had taken place. In one experiment six marked leaves of a large 

 potted plant were inoculated in the following way. A minute drop of 

 distilled water was placed on the upper surface of the leaf, and a number 

 of conidia were placed on the drop by means of a finely pointed glass rod. 

 The plant was not covered over, but placed in a greenhouse at the 

 temperature of 64° F. ; the drops of water evaporated in the course of an 

 hour or so, and the conidia were thus deposited on the epidermis of the 

 leaf. By the second day four of the inoculated leaves showed clear signs 

 of having become infected, minute radiating mycelial hyphre proceeding 

 from the sown conidia. By the third day all the six leaves showed signs 

 of being virulently infected. By the tenth day each of the leaves bore 

 several large radiating patches of mycelium, with many hundreds of ripe 

 conidiophores and conidia, massed together towards the centre of each 

 patch. All the control leaves were free. By the 16th day several of the 

 young control leaves had become inoculated with conidia blown or fallen 

 from the densely powdery Oidrnm-patches on the infected leaves. On a 

 control potted plant, also, which had been placed by the side of the 

 inoculated plant, two leaves had now become spontaneously infected from 

 the same source. By the 29th day (June 1) thirty-seven leaves of the 



