DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 487 



twenty-eight days on leaves and in from nine to thirty-one days on 

 stems. E. F. Smith obtained with needle punctures first signs of 

 disease in fourteen to twenty-one days. In a study of the morbid 

 anatomy of the cabbage, it has been found that the parasite is 

 confined for some time to the vascular system and even to particular 

 leaf traces or bundles, especially to the spiral and reticulated vessels, 

 which are very often filled with incalculable numbers of this organism. 

 Later, as the walls of the vessels are destroyed, the organism finds its 

 way into the surrounding parenchyma. Pseudomonas brassicoe is 

 sometimes motile, especially when taken from the plant, and is 

 examined in a hanging drop of water. Its measurements are 0.7 to 

 3.0/i by 0.4 to 0.5^. It is often somewhat irregular in shape. The 

 flagella is several times the length of the cell and arises at or near the 

 end. The organism is wax-yellow, changing to a dirty yellow-brown 

 in old cultures. 



The treatment of this disease falls principally under the head of 

 restriction and prevention. Seasonal variations are found and the 

 organism thrives well in cool, moist lands. Underdrainage of soils 

 might prove advantageous in wet seasons. The diseased plants should 

 not find their way into the manure heap, but all refuse should be de- 

 stroyed. As E. F. Smith puts it, "Avoid infected seed, soil and manure; 

 destroy insect carriers of infection, if the plants are attacked." Crop 

 rotation is advantageous. Soaking the seed for fifteen minutes in a 

 solution of mercuric chloride (one tablet to a pint of water) should be 

 practiced. 



Club-root {Plasmodiophora brassiccB, Wor.) This disease, which 

 has been known for a hundred years, has received a number of 

 names, such as fingers and toes, Anbury, Hanbury (England), Kohl- 

 hernie (Germany), maladie digitoire (France) Kapoustnaja Kila 

 Russia). (The organism causes unsightly and destructive root dis- 

 ease of cruciferous plants, such as cabbage, Brussels sprouts, turnips, 

 rutabagas, radishes and certain mustards (Fig. 169). The parasite is 

 a slime mould (Myxomycetes) named by Woronin {Plasmodiophora 

 hrassicce). It lives in the parenchymatous cells, often in the vicinity 

 of the cambium, and an abnormal development of phloem is notice- 

 able. The infested cells are grouped together into packets and their 

 contents are at first fluid, then turbid and granular, assuming the 

 amoeboid form with distinct nuclei. The amoeba are increased by 



