A Disease of Currant Canes. 



25 



II. THE BOTANICAL CHARACTER OF THE DISEASE. 



The Fungus. 



On a great majority of the dead canes the pink tubercles of a fungus of 

 the genus Tubercularia were present (Fig. 3, a). They occurred most 

 abundantly near the base of the stalk, but occasionally were found high up 

 on the stem. Very few bushes were seen which had no tubercles on any of 

 the canes. Sometimes they were present on much diseased stems not com- 

 pletely dead. In no case were they present on healthy plants. The tuber- 

 cles were sufficiently abundant and so distributed on the diseased and dead 

 stems as to render it probable that the fungus produced the disease and 

 caused the death of the plants. A careful search was made for perithecial 

 forms, but they were found on only a single plant. These with several speci- 

 mens of the Tubercularia were collected for study. 



An examination showed the tubercles to be the fruiting bodies of a well 

 known species, Tubercularia vulgaris, Tode. Careful sections were made 

 through the wood and 

 tubercles to determine the 

 connection of the latter 

 with the tissues of the 

 host (Fig. 4). Examined 

 under the 

 microscope, 

 one of these 

 sections 

 shows that 

 the vegeta- 

 tive part of 

 the fungus 

 consists of a 

 delicate 

 threa d-1 i k e 

 mycelium 

 spreading 

 abundantly 

 through the 



tissues of the currant stem. The depredations are confined to the younger 

 tissues of the host, within which it forms a wide weft between the cells. It 

 thrives well in the inner bark or cambium layer, thus cutting off the nutri- 

 ment and causing the death of the plant. The cells affected by the myce- 

 lium are much disintegrated and turn brown. 



The hidden mass of mycelium coursing through the tissues is the part that 

 is destructive to the currant plant, since this is the only portion of the fungus 

 that absorbs nutriment. The pink tubercles are the fruiting organs of the 

 fungus. In their formation numerous threads of the mycelium turn out- 

 ward from the bark as a bundle of closely compacted parallel filaments. As 



4. Longitudinal section of a tubercle of Tubercu ria. 



