INCREASE OF THE AMERICAN GOOSEBERRY-MILDEW. 



599 



powdery mildew of the Gooseberry (S. mors-uvce) sometimes attacks 

 Currants. At Ripley, Chautauqua County, we saw this mildew in two 

 plantations of Currants. In one case the plants were unusually thrifty 

 and growing in a Plum orchard. On many plants the mildew attacked 

 the leaves at the ends of the canes, and on a few plants it also attacked 

 the berries, covering them with a brown felt-like growth." The following 

 additional information has been supplied to me by Prof. F. C. Stewart, of 

 the New York Agric. Exper. Station: — "In the instance referred to in 

 my Bulletin, S. mors-uvce was on cultivated Red Currant, Bibes rubrum. 

 I have never seen it on B. nigrum, and I think not on the White Currant. 

 In New York it occurs quite frequently on B. rubrum in small quantity, 

 and occasionally it is sufficiently abundant to be destructive. In my 

 notes I have a record of an instance in which this fungus was destructive 

 to Red Currants at Highland (in the Hudson River Valley) in 1897. The 

 variety of Currant was ' May's Victoria.' In the case mentioned in my 

 Bulletin the damage was slight, but the owner informed me that in 

 former seasons it had sometimes been destructive. I am confident that 

 there are other published references to its occurrence on Currants in the 

 United States, but am sorry to say that in a hasty examination of the 

 literature I have failed to find any." Specimens of S. mors-uvce attack- 

 ing the Red Currant were kindly communicated by Prof. Stewart, and are 

 now deposited in the Kew Herbarium. In these the fungus is abundant 

 in its conidial (Oidium) stage on the leaves of the young shoots, and in 

 the perithecial stage completely invests the young berries with a thick 

 dark-brown felted covering of mycelium. 



On June 13 of the present year Mr. Nixon sent me from Ballymena 

 some Gooseberries thickly covered over with a growth of <S'. mors-uvce in 

 its conidial condition. In this stage the fungus is wholly white, and is 

 composed of delicate creeping mycelial threads, from which suckers are 

 sent into the epidermal cells of the leaves and berries. This mycelium 

 bears at short intervals a great number of closely-crowded, erect, simple 

 branches, the conidiophores, and at the apex of each conidiophore the 

 conidia are produced in a long bead-like chain by abstraction in basipetal 

 succession. The conidia are broadly elliptic in shape, and measure 27-31 

 x 18-20 jj. ; they are colourless and hyaline, and filled with vacuolated 

 protoplasm, in which minute nbrosin bodies occur. The conidia are 

 produced great number, so that the affected parts quickly become 

 covered with a powdery mass of glistening white conidia. A representa- 

 tion of S. niors-uvce in its conidial stage is given on p. 600. 



Using the material sent by Mr. Nixon, I was successful in infecting 

 another species of Bibes, viz., B. Cynosbati, with the conidia of S. mors- 

 uvce growing on B. Grossularice. The plant of B. Cynosbati that was 

 thus infected was kept in a moist atmosphere under a bell-jar. Two 

 young leaves and several old leaves were inoculated on the upper and 

 under surface, also a portion of a young stem. On the tenth day after 

 inoculation both the young leaves bore — on the under surface only — small 

 patches of mycelium with numerous small groups of well-grown conidio- 

 phores with chains of ripe spores. No infection occurred on the old 

 leaves or on the stem. The above experiment is of interest as showing 

 that in the case of the form of S. mors-uvce on Bibes Grossularice the 



