ROSE CANKER AND ITS CONTROL. 23 



then removed with a flamed needle to a flask of sterile water, washed, and trans- 

 ferred to a potato agar slant — or sometimes poured plates are used. One or two 

 drops of lactic acid are added to the tube of agar when slanted. The acid not only 

 prevents growth of bacteria, but also seems to make the medium more favorable 

 for the growth of Cylindrocladium. Occasionally other agars, such as corn meal, 

 oat, lima bean, Czapek's and Cook's No. 2, have been successfully used, and there 

 is no objection to them. The almost constant use of potato agar in the present 

 investigation is due more to habit and convenience than to any advantage over 

 other media. In the ease of small initial cankers the epidermis was not peeled 

 off. The mycelium grows up into the air and into the agar very quickly, and after 

 some experience one is able with the naked eye to distinguish within twenty-four 

 hours the growth of Cylindrocladium from that of other fungi he is apt to meet 

 with on roses. But if there is any doubt, he has but to wait another day or two, 

 and spores are produced by which this fungus can be absolutely identified. 



Other methods of isolation besides tissue transfers have been successfully used. 

 Where spores are present, or where they have been developed in moist chambers, 

 cultures are very easily made by touching them with the tip of a sterile platinum 

 needle, — first thrusting the needle into the agar so that more spores will adhere, — 

 and then transferring to agar slants. When the sclerotia were first discovered on 

 the cankers there was some question as to their connection with Cylindrocladium. 

 Some of them were picked out under the binoculars with a sterile needle, freed 

 from all clinging rose tissue, washed in sterile water, and transferred to agar plates. 

 In this way, also, pure cultures were obtained. 



By the first method described, the organism has been isolated in pure 

 culture from hundreds of typical cankers. In order to determine the very 

 youngest stages, a number of stems showing the little round lesions (de- 

 scribed under "Symptoms"), from the size of a pin point to several 

 millimeters in diameter, were brought into the laboratory, washed merely 

 with sterile water, and transfers made as above. Pure cultures were 

 obtained from even the smallest of them. 



The relation of the pathogene to dead stubs was also determined in 

 this way. After the flower is cut, one or more shoots quickly grow out 

 from below the cut end of the stem. The topmost one, however, is usually 

 some distance below the cut surface, and a useless stub is left from 1 inch 

 to 3 or 4 inches long. This stub usually dies slowly from the apex back 

 to the first branch, where it is apt to stop. When the canker disease is 

 prevalent in the house, however, the dying frequently does not stop at 

 the first shoot but continues down the stem, and the shoots die as they 

 are encircled by the descending dead area. Frequently the fruiting bodies 

 of various species of fungi, such as Pestalozzia, Phoma, etc., can be found 

 on these stubs, but in other cases no spores could be found. A large 

 number of them were collected from a house known to be infested, and 

 transfers made. Cylindrocladium was obtained from over half of them. 

 After they were found to be infested in some cases, more attention was 

 directed to them and the sclerotia frequently observed. It was from 

 these sclerotia that the pure cultures mentioned above were obtained. 



Study of the fungus in pure culture will be described later. 



3. Plants were inoculated in four different wavs: — 



