STUDIES ON CLUBROOT OF CRUCIFEROUS PLANTS 445 



The fact that only the small swellings show no contamination might 

 be attributed to the penetration of the mercuric chloride. In order to 

 avoid this source of error, the time of treatment was reduced from ten 

 minutes to five, and even to three, or was dispensed with entirely, the roots 

 being soaked for three hours in water that had been standing over calcium 

 hypochlorite for two hours and then decanted. The results were the same. 



Another possible hindrance to the appearance of colonies at first might 

 have been the medium, which was nutrient agar. In order to eliminate 

 this objection, later cultures were made both in potato agar and in a 

 medium made from the extract of healthy cabbage roots like that used 

 successfully by Kleimenov (1912). No bacterial growths were obtained. 



Bacteria have been found in large roots similar to those that Pinoy 

 used; but Pinoy obtained a coccus, while the most prevalent form in 

 the cultures of the writer has been a very motile rod-shaped bacterium 

 producing yellowish, opalescent colonies on the various media. In test 

 tubes containing disinfected diseased roots this organism readily produces 

 a soft rot and thus liberates the spores of the slime mold. It is well 

 known that the epidermis is soon ruptured after swelling begins, and from 

 all indications the conditions are propitious for the entrance of any 

 T organisms that may be in the soil. This is doubly true for any that 

 find exposed cabbage tissue a favorable substratum on which to reproduce, 

 as does evidently the bacterium mentioned above. These series of cultures 

 tend to show that bacteria do not enter with the swarm-spore, as Pinoy 

 (1905) believes, but that the disease must advance to a certain stage 

 before the bacteria can gain entrance. The above experiments are 

 perhaps in themselves not sufficient proof, especially since they bear 

 on the negative side of the question. To these, however, are to be added 

 the following data: 



The writer has found that spores germinate better if they have been 

 exposed to cold or to drying for a short time before being placed in a 

 warm oven at a temperature of from 2 7 to 30 C. ; and that the best medium 

 tested is water that has been filtered thru muck soil. Accordingly diseased 

 roots were washed, treated with either mercuric chloride or calcium 

 hypochlorite, placed in sterilized, cotton-plugged test tubes, and left 

 in the ice box for seven days. At the end of that time they were cut 

 into pieces with a flamed scalpel and some of the sterilized muck filtrate 

 was added, after which the roots were placed in the incubator for six 

 hours. Before making mounts to examine the material, a loopful of the 

 filtrate was transferred to each of two petri dishes, which were then poured 

 with nutrient agar. This was done in order to determine with certainty 

 whether or not bacteria were present. Germination was fully as good 

 when the bacteria were not present as when they were. This is in direct 



