452 



New Phoma Disease of the Swede. 



Avhich soon became septate, and then, branching and rebranch- 

 ing repeatedly, grew eventually into a dense white mycelium. 

 If the spores were not sown too thickly, as they germinated, 

 it was possible under the microscope to remove the young 

 mycelium growing from a single spore and transfer it for 



Fig. 6. — a and b — Spores germinating on a gelatine medium three days after sewing,. 

 (Leitz obj. 7, o.c. 2). c— Spore germinating on the host plant ; the germ-tube is- 

 seen entering an external cell. (Zeiss E, oc. 3). 



cultivation upon special media. Many cultures were made- 

 in this way upon various nutrient gelatines, but, so far,, 

 these have not resulted in the production of any organs of" 

 fructification.* 



When the spores were sown upon a piece of living swede 

 germination also readily took place. Part of a perfectly" 

 sound root was prepared by washing the rind in a weak 

 solution of corrosive sublimate to sterilise it,f and then 

 thoroughly washing away the antiseptic with several changes- 

 of sterile water; small blocks were then cut from it with a 

 sterile knife. When placed upon the rind of these blocks 

 the spores germinated exactly as on gelatine, and the germ- 

 tube quickly effected an entrance into the external cells- 

 Fig. 6 c) ; the hyphae then branching and making their way 

 from cell to cell, soon permeated the cells and intercellular 

 spaces (Fig. 3), causing the death of the protoplasm and 



It has not been thought advisable in a short paper of this description to give an> 

 account of the special media employed, or minute details of the methods of steriliza- 

 tion. Suffice it to say that every proper precaution has been taken throughout to. 

 ensure pure cultivations. 



t It might be objected that the washing with corrosive sublimate would destroy 

 the cells, and the fungus might thus enter as a saprophyte, but the protoplasm would 

 be protected by the external cell-walls, and a careful macroscopic search failed to- 

 detect any injury to the protoplasm. The conidda germinate and enter the host 

 quite as readily when this aseptic treatment has not been, adopted* 



C 



