54 



MICROBIAL DISEASES OF PLANTS. 



So far as is known, the causal organism enters the twigs and leaves of 

 the olive through wounds, and there produces roughened, wart-like 

 swellings. The growth of the knots usually begins in the spring, and 

 later in the season, if the trees are badly diseased, they show scant 

 foliage, limited growth, and occasionally dead branches, especially where 

 the galls have entirely encircled the twigs. 



A B 



/#/#!; 



/|rV **Q a ? c "^ 



FIG. 94. Plasmodiophora brassica. A, individuals undergoing mitotic division 

 (at the top is the nucleus of the plant cell). B, two plant cells with developed and 

 partly developed spores. (After Prcrwazek, from Doflein.) 



"FINGERS AND TOES" OF CABBAGES.* 



A species of a genus of Rhizopoda, Plasmodiophora brassica, is the aause 

 of a common disease of the roots of cabbages and of other cruciferous 



*Prepared by J. L. Todd. 



