

J 9°9] BRIEFER ARTICLES .„ 



what and becomes soft and disintegrated, resulting in the death of the more 

 distal portions of the plant. 



Variety of carnations affected.— A striking feature of this disease is its 

 tendency to infect to a large degree one variety, the Mrs. Thomas 

 W. Lawson, to the exemption of others. In all cases which have 

 come to our notice, it has been this variety solely which was diseased- 

 moreover, the only records that we find of the disease imply the same' 

 susceptibility. 6 



The causal fungus .— Throughout the diseased tissue of all spots occurs 

 in great abundance a characteristic, dark, branching, septate mycelium 

 (fig- 3)- The surfaces of diseased spots in periods later than their earliest 

 youth present an abundance of black cespitose hyphae arising from the 

 stomata (fig. 4 ). Spores of the Alternaria type are found in abundance 

 (figs- 5, 6), both in situ upon these hyphae, and strewn over the surface of the 

 diseased spots between the hyphal bases. The character and arrangement 

 of the hyphae are shown in figs, y and 8. This fungus was constantly 

 associated with the disease, and no other fungus was found. The pre- 

 sumptive evidence was therefore very strong that this fungus was the 

 cause of the disease. In view of the often saprophytic habit of Alternaria, 



conclusions on this point would not be valid without evidence from inocula- 

 tions. 



Inoculations. — The fungus was easily isolated by direct transfer of 

 spores from the diseased spots to carnation-leaf agar plates. 



On October 27 numerous inoculations were made upon two plants 

 under bell jars, using small pieces of agar, bearing spores and mycelium. 

 One of the plants was left uninjured and the inoculum was placed in the 

 axils of the leaves; in the majority of these cases the inoculations resulted 

 m infection. The other plant was injured by the prick of a needle at the 

 Point of inoculation. In these cases about two-thirds of the inoculations 



ere successful. Inoculations with spore suspension were also made upon 



v e branches each, of two other plants, and each was covered by a large 

 test-tube plugged around the stem with cotton to preserve a humid atmos- 

 P ere. As in the former cases, the inoculations on one plant were at injured 

 Points, and those on the other plant were at uninjured points. The results 



°m these spore inoculations were the same as in the cases of inoculations 

 agar blocks. When these inoculations were made, others were made 



Pon six other plants from the same spore suspensions, but the plants were 

 covered or injured in any way. Following these last inoculations no signs 



Of th A' ' J J O O 



disease were seen. It seems from these experiments that the injured 



6 Orton, W. A., Yearbook, U. S. Dept. Agric. 1905:611. 



