BLACK ROT OF CRUCIFEROUS PLANTS. 



311 



petioles, but neither by suction nor by pressure with mercury could he get them higher than 

 about 2 cm. The stain passed farther but not the bacteria. According to Hecke the bac- 

 terial infection passed upward in certain inoculated kohlrabi leaves 5 cm. in the time 

 required to pass downward 2.5 cm. This more rapid upward movement is attributed by 

 him to the effect of the transpiration stream. 



Weather conditions favorable to rapid growth are also favorable to the spread of this 

 disease. When two sets of plants are inoculated in the same manner, the one receiving 

 large quantities of water and the other less amounts, the former contract the disease more 

 readily and the organism also passes through the tissues with greater rapidity (Russell). 



Varietal resistance to this disease, and the resistance of particular individuals 

 within the variety, are subjects deserving of careful attention. Russell states that "In all 

 probability there is but very little dif- 

 ference in susceptibility, all varieties 

 readily yielding to the disease, if the 

 causal organism is once present." 

 Many cabbage growers think differ- 

 ently, but so far as the writer has had 

 opportunity to examine into the 

 matter himself he has found the 

 statements of particular growers that 

 this or that variety was specially 

 subject based only on isolated obser- 

 vations and easily overthrown by 

 other observations in the same lo- 

 cality or some other. In experiments 

 with kohlrabi Hecke found that the 

 "Vienna Glaskohlrabi," which ma- 

 tures quickly, is less Hkely to show 

 the disease in the fleshy part as the 

 result of leaf-inoculations, than is 

 the slowly maturing variety known 

 as "Goliath . " Generally the farmer 

 thinks that variety most subject 

 which he happens to have planted on 

 infected land, while as a matter of 

 fact on the very next farm the con- 

 ditions may be reversed. Nothing 

 here said should be construed into a 

 denial of difference in behavior, but 

 only regarded as a reason for caution 

 in drawing conclusions, it being quite 



in line with what we know of other diseases to suppose there are tendencies to resistance, 

 especially in particular plants, which might be increased and made of economic importance. 



According to Russell, cauliflower is the most susceptible plant, while turnips and 

 rutabagas are not very susceptible. The writer found radishes rather resistant. 



In North Holland, according to Ritzema Bos, the disease was most prevalent in red 

 cabbage in 1900, but in Savoy cabbage in 1901 . 



Fig. 109.* 



*FlG. 109. — Portion of a cauliflower-petiole in cross-section, showing destruction cf the xylem portion of several 

 bundles by Bacterium campesire. In lower left-hand part of figure bacteria may also be seen wedging apart parenchyma 

 cells. Result of a pure culture inoculation made into blade of leaf by means of needle-pricks. Material fixed in alcohol, 

 infiltrated in parafiBn, sections stained with carbol-fuchsin, and drawing made from a photomicrograph, x 190. Slide 

 1 18-5. For a small portion of this section more highly magnified see fig. 1 10. For a longitudinal section through a 

 similar cauliflower-petiole see vol. i, fig. 7. 



