ROSE CANKER AND ITS CONTROL. 33 



in the course of the investigation it was suspected that it might have 

 been brought over from Europe on Manetti stocks, which are used almost 

 exchisively by rose growers for gi-afting. The Manetti is moderately 

 susceptible to the disease, as may be readily determined by examination 

 of Manetti shoots coming from below the graft in a badly diseased house. 

 Pure cultures have frequently been made from these shoots. Massey 

 (1917) also made infection experiments and found Manetti roses suscepti- 

 ble. In the course of these investigations hundreds of Manetti stocks 

 from Scotland were examined for lesions, numerous tissue plants were 

 made, hundreds more were kept in moist chambers to bring out the 

 fungus, and thousands of them watched carefully for a year after being 

 planted in sterilized soil in order to see whether the disease developed. 

 All results were negative, and up to the present we have no reason to 

 suspect that the fungus is being imported on Manetti stock. It would 

 be very helpful if we knew how widely the fungus is distributed over 

 this country in its natural state, and whether it is being carried into the 

 houses again and again. Various investigators have worked on the 

 fungous flora of the soil and published lists of species isolated, but none 

 of them mentions Cylindrocladium. This may indicate that it is only 

 local in its distribution, or may be due merely to difficulties of isolating 

 it. There seems to be little doubt that it infests the soil about rose 

 houses where the disease occurs and where infested soil has been dumped 

 out. 



2. Spread from One Grower to Another. 



Plants are continually being sent from one grower to another. Small 

 cankers on these would be overlooked even if the sender was familiar 

 with the disease. Not only could the mycelium be sent in the plant 

 itself, but particles of soil adhering to the plants could easily carry it. 

 It has been proved by laboratory tests that infested particles of soil 

 may be kept dry for at least three months, and probably longer, without 

 killing the mycelium. The disease may be spread in other ways, but 

 this one would be sufficient to account for the present known distribution. 



3. Local Dissemination. 



There are a number of ways in which the fungus spreads from one 

 part of a house to another, or from one plant to another, (a) It may 

 grow for long distances through the soil and enter the plant below the 

 surface of the soil. That infection can take place in this way has been 

 repeatedly proved by setting clean plants in infested soil and thus pro- 

 ducing the disease on them. (6) If the fungus is in the potting soil it would 

 be effectually distributed in the beds when the plants were transplanted 

 to them, (c) Where "own-root" plants are grown the soil in the cutting 

 bench maj^ be infested, and the disease is then carried with the cuttings 

 when they are planted in the benches, (d) It is easily carried from one 

 part of the house to another on tools, clothes and shoes of workmen. 



