ON A FUNGUS DISEASE OF EUONYMUS JAPONICUS LTNN. F 439 



with a razor, or by a bruise, infection resulted. The fungus proved 

 unable to infect leaves of E. evropceus, E. chinensis, and E. amcricanus. 



If affected shrubs of E. japonicus are examined, it will usually be 

 found that only the younger, brighter green leaves bear the fungus, and 

 that the old dark-green leaves are not attacked. A number of inoculation- 

 experiments which have been carried out have shown that the conidia are 

 unable, under ordinary conditions, to infect these old leaves. I have 

 proved, however, that such leaves, when wounded so as to expose the 

 inner tissues, become susceptible to the disease. Two cases, out of a 

 large number of experiments made, may be mentioned here. In the first 

 experiment two oldish leaves, 5 cm. long, of E. japonicus var. ovatus 

 aureus were inoculated, on May 5, with conidia sown on the uninjured 

 upper epidermis. No infection had occurred at the end of twelve days. 

 The same leaves were then inoculated again at another spot on the 

 uninjured upper epidermis ; no trace of any infection had occurred at the 

 end of seven days. The two leaves were now wounded by removing a 

 small piece of the upper epidermis with a razor, and conidia, from the 

 same source as those previously used, were sown on the mesophyll cells 

 thus exposed, and also on uninjured epidermal cells at a little distance 

 away. On the twelfth day after inoculation one of the leaves was 

 strongly infected at the cut place, the exposed mesophyll cells bearing a 

 vigorous patch of mycelium with crowded clusters of conidiophores. No 

 infection resulted elsewhere. 



In the second experiment four young vivid-green leaves of E. japonicus 

 were inoculated on the uninjured upper epidermis. Also four old dark- 

 green leaves, from the same shoot, were inoculated (with conidia from the 

 same source) in the following manner : On each leaf conidia were placed 

 on a patch of uninjured epidermal cells on one side of the midrib, and 

 opposite them, on the other side of the midrib, a cut removing a patch of 

 epidermal cells was made with a razor, and conidia sown on the exposed 

 mesophyll-cells. Inoculation was made on August 6. By August 13 

 virulent infection was apparent on the four young leaves, which now bore 

 numerous large vigorous patches of mycelium with conidiophores. No 

 infection had resulted on the uninjured epidermis of any of the four old 

 leaves, but two of the leaves bore at the wounded place small patches of 

 mycelium with numerous clusters of ripe conidiophores and powdery 

 masses of accumulated conidia. 



The chief interest for horticulturists in connection with the above fact 

 is the proof it affords of the necessity of protecting plants as far as possible 

 from all sources of injury. It cannot be doubted that the injury due to the 

 attacks of animals, or occasioned by frost, hail, or gales of wind, may often 

 be the cause which renders a leaf, hitherto resistent, susceptible to a fungus 

 disease. I have frequently observed, in the case of the disease caused by 

 mildew on Turnips, Roses, Grasses, Peas, &c, that the most severe outbreaks 

 occur on plants which are or have been overrun by insect parasites.* I 

 have recently shown (8) by inoculation-experiments that the attacks of 

 slugs may cause injuries to Barley leaves which render them susceptible in 



* A recent paper by J. R. Jungner in the Zeitschr. f. Pflamenkrankh., 1904, p. 321, 

 may be consulted on the subject of the inter-connection, in many cases, of plant 

 and animal parasites. 



