EFFECT ON THE CALLA. 



15 



EFFECT OF THE ORGANISM ON THE CALLA. 



As already stated, the part of the j)hiiit usually attacked first is the 

 upper portion of the corni at or just helow tiie surface of tlic ground. 

 A microscopic examination of the atiected part, whether root, corm, 

 leafstalk, or flower stalk, shows that the organisms occu]\v the intercel- 

 lular spaces and by some means dissolve the intercellular layer, causing 

 the cells to separate easily, so that when the diseased tissue is j)laced in 

 a litiuid each cell floats out by itself. The cell wall, however, remains 

 intact, ))ut the cell contents are contracted. The rapidity with which 

 the disease advances depends to a large extent upon the external con- 

 ditions surrounding the plants, lender favorable conditions a warm 



Fig. 3.— Calla leaf twenty-two 

 hours after inoculating with 

 the ealla organism. The point 

 of inoculation is shown bv X. 



Fig. 4. — Calla flower stalk twenty-two hours after 

 inoculating with the calla organi.'<m. The point 

 of inoculation is shown by X. 



atmosphere and an abundance of moisture — the disease ma}-^ completely 

 rot the corm in. from three to four days, while under less favorable 

 conditions it may be several weeks in destroying the corm, or, indeed, 

 the progress of the disease may be entirely arrested for a period of 

 several months. While the organism usuallv attacks the corm fir.st, 

 it may also attack either the leafstalk or the flower stalk and cause it 

 to become discolored and decayed. (See flgs. 3 and 4.) 



MORPHOLOGICAL CHARACTERS OF THE ORGANISM. 



The organism which causes the rotting of the calla corm is a very 

 short rod, with rounded ends, as shown in figure 5, and also in 

 Plate 11, figure 1. The width of the rods is very nearly uniform. 



