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March 13, 1919. 



The Florists' Revkw 



17 



the case of some varieties on all the 

 aerial parts of the plant, the disease is 

 confined practically entirely to the 

 leaves. The more or less circular spots 

 toAj reach a diameter of a centimeter 

 or more, are black in color and are char- 

 acterized by radiate-fibrillose margins. 

 They usually appear late in the spring or 

 early in the summer and occur only on 

 the upper surface of the leaf. The spots 

 are small at first but increase in size as 

 the disease progresses. Often a number 

 of them coalesce and in severe attacks 

 the entire leaf may be covered with 

 large dark patches. In the latter part 

 of the season the spots frequently grow 

 light in color and dry in the center, 

 showing this part of the leaf to be en- 

 tirely dead. 



Produces Premature DefoUatiou. 



Very commonly the leaf tissue adja- 

 cent to the black spots becomes chlorotic 

 before the leaves fall from the plant, 

 and not uncommonly all of the uninvad- 

 ed tissue becomes yellow before defo- 

 liation occurs. The leaflets may turn 

 yellow in spots, while sometimes the 

 yellow area is limited to a band outside 

 the black spot. Commonly, and espe- 

 cially during the autumn, the yellow 

 color appears at the apex of the leaflets, 

 whence it spreads downward and is 

 succeeded by brown. A leaf with a 

 green base and brown tip with a yellow 

 band between is very characteristic of 

 this disease. 



Premature defoliation is one of the 

 most pronounced characteristics of this 

 disease. Affected leaves may fall be- 

 fore they turn yellow, the slightest jar 

 or breeze often causing them to drop in 

 great numbers. Diseased plants usually 

 have a partially defoliated appearance. 



The size and shape of the black spots, 

 the rapidity and the extent of defolia- 

 tion of plants, seem to vary with the 

 variety. No reports of observations on 

 these points are to be found in litera- 

 ture. 



Black spot of the rose is caused by a 

 fungous parasite, Diplocarpon rosae 

 "Wolf, long known under the name of 

 Actinonema rosae (Lib.) Fries. 



Life History of the Parasite. 



Diplocarpon rosae has two phases in 

 its life cycle — an actively parasitic 

 phase developed during the summer and 

 a saprophytic phase in which the fun- 

 gus lives during the winter on dead and 

 decaying tissue. 



An examination of the lesions on the 

 leaves during the summer will show the 

 presence of small black pustules which 

 are the fruit-bodies of the fungus. In 

 these fruit-bodies the conidia or sum- 

 mer spores are born. These spores are 

 matured rapidly during the growing 

 season and are blown about by the wind, 

 thus distributing the fungus and bring- 

 ing about successive infections with new 

 crops of conidia. This phase of the fun- 

 gus is the one most commonly met with 

 and has been known under the name of 

 Actinonema rosae (Lib.) Fries for many 

 years. 



During the winter the sexual or ascig- 

 erous phase develops. When leaves af- 

 fected with black spot fall to the ground 

 during the summer and autumn, the fun- 

 gus does not die, but lives over winter 

 as a normal saprophyte. If examined 

 microscopically during the spring it 

 will be found that another spore-form 

 has developed. In this stage spherical 

 fruit-bodies (perithecia) bearing nu- 



JOHN a. ESLEB. ^ 



EVERY grower in the United States who has had his establishment more or less 

 damaged by hail and has been recompensed for the loss by the Florists' Hail 

 Association has reason to be thankful to John G. Esler, of Saddle Biver, N. J. 

 When the Florists' Hail Association was conceived at the S. A. F. convention in 

 Philadelphia in 1886, Mr. Esler was elected its secretary and ever since has held 

 the job. He was instrumental in securing a change in the laws of New Jersey 

 which made the association possible, has worked year in and year out to build it 

 up and never yet has received more than nominal compensation. Mr. Esler is 72 

 years of age, but doesn't know it. He was flrst interested in the florists' business 

 more than forty years ago and is one of the charter members of the New York 

 Florists' Club. Mr. Esler has attended every annual convention of the S. A. F.' 

 except the first. One source of satisfaction to Mr. Esler is the fact that he has 

 materially assisted in developing one of the most successful cooperative insurance 

 organizations in the world. 



merous sacs or asci, each of which con- 

 tains eight ascospores, are produced in 

 the old leaves lying about on the ground. 

 These fruit-bodies serve to carry the 

 fungus over the winter, the spores being 

 mature at the time of opening of rose 

 leaves in the spring. 



Inoculation. 



The old leaves on the ground are to 

 be considered the chief source of pri- 

 mary inoculum in the spring. However, 

 the fungus is carried over winter on 

 plants under glass from which conidia 

 could be carried readily by the wind to 

 the newly developing leaves on outdoor 

 plants. Growers frequently buy pot- 

 grown plants in the spring to plant in 

 their gardens and are likely to thus 



carry the fungus to the plants which 

 were outdoors during the winter. Scrib- 

 ner, who was acquainted only with the 

 asexual stage, suggests that the spores 

 (asexual) lodge on the buds in the au- 

 tumn and remain there dormant until 

 the leaves have expanded the following 

 autumn. In warmer climates the con- 

 idia may live over winter and serve as 

 inoculum the following spring. No spe- 

 cial investigations on this point have 

 been reported in literature. Wolf could 

 find in wintered material no acervuli 

 which were bearing conidia. It seems 

 very improbable that the conidia winter 

 in any sections of Massachusetts or 

 places having similar temperatures. The 

 evidence derived from observations on 

 the parasite warrant the conclusion that, 



