32 



BACTERIA IN RELATION TO PLANT DISEASES. 



of cabbages and the basal part of the stem are generally quite woody; these parts, therefore, 

 are not usually affected except in young plants. Sometimes a well-grown cabbage plant 

 badly diseased in the foliage will show a few insignificant black specks in its woody base, 

 but more commonly there will be none whatever unless the plant has been diseased from 

 the time it was a seedling. In turnips the most striking signs are usually in the fleshy root 

 which may not be well developed, if attacked early in the season, and which is often hollowed 

 out into considerable cavities even when there are no external signs other than dwarfing and 



Fig. 99.* 



leaf-injury (fig 106). In turnips examined by the writer in August, 1896, the disease had 

 so seriously interfered with growth that the underground parts were more like carrots in 

 shape than like turnips. In the cauliflower and other plants mentioned the signs are much 

 the same as in the cabbage, the black veining being more or less conspicuous, as the case may be. 

 Marginal leaf-infections are very common in cabbage (plate 2 and fig. 9) and in charlock. 

 Thousands of such infections have been observed by the writer. In kohlrabi the black 



*Fig. 99. Effect of bacterial black rot on cauliflower Plantsvery badly dwarfed; many leaves fallen. Collected 

 at Miami, I " 1 ; i . , Mar. 1904. 



