Disease of the Turnip (Brassica napus). 



447 



natural firmness and clear regularity of outline, being bulgy and dis- 

 tended in places ; the dissolution of the cells is very apparent along 

 the middle lamella, and the whole appearance of the section corre- 

 sponds exactly with those taken from turnips found affected by the rot 

 in the fields. The sections contained in the boiled fluid exhibited 

 none of the appearances described above, and the cell-walls remained 

 perfectly normal. It is thus evident that the bacterium secretes an 

 enzyme which dissolves the middle lamella and causes the softening 

 and swelling of the cell-wall. Fig. 2 represents a single cell from a 



Fig. 2. Cell immersed for sixteen hours in an unboiled solution of the cytase. 

 Thickness of cell-wall, 2 p. at x x (Zeiss, E. oc. 2). 



section immersed in the filtered, unboiled liquid for sixteen hours. 

 Fig. 3 shows one after an immersion of forty hours. The thickness of 



Fig. 3. Section immersed for forty-two Lours in unboiled solution of the cjtase. 

 Thickness of wall, 5'3 p. at x x (Zeiss, E. oc. 2). 



the walls was 2 /u, and 5 -3 /A respectively. (I should remark here that 

 these sections were cut out of season from old turnips in which the 

 walls would be more resistant, and this would account for the; rela- 



