PLATE 1 
INFLUENCE OF SOIL TEMPERATURE ON CLUBROOT OF 
CABBAGE 
Note absence of disease at lower temperatures 6° and 9°, and the clubs at 
the higher temperatures, 12° and 15° C. 
Plants grown eight weeks, at the soil temperatures indicated in a clay loam 
soil (soil A of the text, p. 552) uniformly infested with the clubroot organism. 
The air temperature for all alike was about 15° C. This soil was of a nature 
favorable to the development of clubroot and was kept uniformly at a moisture 
content found favorable for the development of the disease, that is 75 per cent of 
the water-holding capacity. The complete absence of clubroot in the two left- 
hand specimens must therefore be attributed solely to the inhibiting influence 
of soil temperature. 
The relative size of these plants also deserves consideration. Note that nor¬ 
mally at this range of soil temperatures with rising temperature there would 
occur a corresponding continued increase in the size of the seedlings (see Plate 2). 
Such normal increase in size is shown in the healthy seedling at 9° C., as com¬ 
pared with that at 6° C. The plant at 12° has evidently suffered some check 
as a result of the clubbing of its roots, and that at 15° has been much stunted 
because of the early and severe infection. 
( 562 ) 
