138 DISEASES OF GLASSHOUSE PLANTS 
calla lily (Richardia) have been troubled by a disease 
which threatened to exterminate their entire stock. 
On some nurseries its hold became so strong that it 
was impossible to grow arums, and the whole of the stock 
had to be burnt. Only after an interval of several 
years was it possible to cultivate this plant again. The 
disease generally shows itself about January, after the 
first lot of blooms has been gathered. First symptoms 
consist of a withering of the leaf apex and a desiccation 
of the entire margin. The desiccation spreads as blotches 
from the margin and the diseased 
leaves die prematurely. The plants 
come to a standstill, do not readily 
produce more flowers, and do not 
react to feeding. j 
An examination of the roots 
shows them to be brown, soft, and 
watery. The rot spreads from the 
roots back into the pseudo-corm 
(Fig. 38), becoming worse as the 
season advances. Quite commonly 
the foliage appears to recover, but 
soon goes back to the diseased ap- 
pearance. This recovery corresponds 
to the production of clean roots, but 
as these are attacked in turn so the 
Mia, 3: gacllue carotovorus LOliage suffers. 
oo The disease is of bacterial causa- 
tion, and isolation has yielded a bacillus indistinguishable 
from B. carotovorus Jones. Townsend has also described 
a soft rot of the calla in America due to B. aroidew, which 
is closely related to B. carotovorus, but our isolations 
appear to differ from B. aroidece Towns. 
Certain methods of control have been devised which 
up to the present have yielded satisfactory results (7). 
The general method is as follows: After the plants have 
been allowed to “dry off” they are shaken out of the 
pots and all soil removed. The adventitious roots are 
