—t 
BLACK ROT OF CRUCIFEROUS PLANTS. my 
petioles, but neither by suction nor by pressure with mercury could he get them higher than 
about 2cm. 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, andthe 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 likely 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 1gor. 
*Fic. 109.—Portion of a cauliflower-petiole in cross-section, showing destruction cf the xylem portion of several 
bundles by Bacterium campestre. In lower left-hand part of figure bacteria may also be seen wedging apart parenchyma 
cells. Resultofapurecultureinoculation made into blade of leaf by means of needle-pricks. Material fixed in alcohol, 
infiltrated in paraffin, sections stained with carbol-fuchsin, and drawing made from a photomicrograph. x 190. Slide 
118-5. Fora small portion of this section more highly magnified see fig. 110. For a longitudinal section through a 
similar cauliflower-petiole see vol. 1, fig. 7. 
