New Phoma Disease of the Swede. 455 



regard to the manner in which the disease is spread by 

 means of the spores, it is obvious that the roots should be 

 carefully examined in the autumn with the object of detect- 

 ing- any indications of disease, and those found to be affected 

 should at once be taken up and destroyed by burning. To 

 leave old roots and leaves lying about is a fatal method of 

 perpetuating disease ; the spores are very readily blown 

 about and carried from field to field, and the rotting roots 

 are bound to be a source of future infection. They may pro- 

 vide the very home required in which to continue the secon- 

 dary life-cycle which so often enables a fungus to exist until 

 the old conditions suitable for its first stage of existence 

 come round once more. Great attention should also be given 

 to ensure a thoroughly dry place for storage, and that as far 

 as practicable there should be a free passage of air through 

 the stored roots, for it is just in moist, warm chambers 

 that the fungus obtains the conditions most suitable to its 

 rapid growth and reproduction. I would, moreover, suggest 

 that the influence of manures and various food substances in 

 the soil on the predisposition to the disease should form an 

 important subject of investigation. In this connection it 

 should be noted that I failed to infect swedes growing in 

 the Botanic Garden in Newcastle, and only succeeded upon 

 roots obtained from Cockle Park. It might be supposed 

 that the special manurial treatment at the latter station 

 rendered the swedes more susceptible to the attack, while 

 those in Newcastle were resistent in a high degree ; and it 

 would be interesting to know whether the proportion of 

 diseased roots in the different plots bore any relation to the 

 different manurial treatment, but at present this point waits 

 further elucidation. 



Characters of the Phoma on the Swede. ' 



Pycnidia. — Numerous, ovoid, black ; about '3 mm. in diameter ; subcutaneous but 

 afterwards exerted, opening by an apical pore. 



Com'dia.— About 4 ju, long, breadth half the length; cylindrical with rounded 

 ends ; emerging from the pycnidia as a globular or vermiform mucilaginous 

 mass of a pale or deep rose colour to bright carmine ; single conidia 

 appear colourless, but when aggregated together are of a distinctly 

 purplish tint. 



