258 EXPERIMENTAL FARMS 



2 GEORGE V., A. 1912 



tally described an affection apparently of this nature in certain localities. This is not 

 surprising when we consider that it is particularly bad in the eastern United States, 

 e.g. in the neighbourhood of Buffalo, not far from the Canadian boundary. Since 

 the disease is at present comparatively restricted in its occurrence and at the same 

 time very characteristic in its appearance we here give an account of it in order that 

 farmers and others may guard against its introduction and also that we may, if pos- 

 sible, obtain more information as to its distribution. We shall be particularly glad 

 to receive suspected specimens or answer inquiries to these end-. 



* 



Appearance and Cause. 



Many kinds of cruciferous plants are liable to suffer from this disease. Amongst 

 cultivated plants, the different varieties of cabbage, turnip, cauliflower and Brussels 

 sprouts are subject to it, and amongst weeds such common ones as Shepherd's Purse, 

 Hedge Mustard and others. The names given to it are more or less descriptive of the 

 character of the malformation induced e.g. club-root, club-foot, clubbing, finger-and- 

 toe, and others of similar significance in other languages. In England it is often 

 known as ' anbury.' The cause of the disease is a minute parasite which invades the 

 tissue of the root system probably by means of the root-hairs. Inside the host, the 

 organism causes the enlargement and division of the attacked cells with the result 

 that swellings of various forms appear. The whole root system may be converted into an 

 irregular, knobbed mass, or the principal roots may retain their distinctness but become 

 much thickened, these different appearances having prompted the different names 

 already alluded to. So far as is known only the root system is attacked. The effect 

 of this abnormal growth is to seriously interfere with the power of the root to absorb 

 the water and other soil constituents. Attacked plants ' flag ' or wilt and either die 

 or only reach a very imperfect development. Ultimately the swollen portions become 

 invaded by other organisms and the plant substance is reduced to a rotten mass, which 

 gives off a very offensive odour. In the meantime, the parasite has changed into 

 mormons numbers of minute resting spores which become in this way distributed 

 through the soil. These resting spores finally germinate and give rise to exceedingly 

 small active spores which again enter a suitable host plant. Although there is no 

 evidence of the organism being able to attack any part of the plant except the root, 

 it is thought the disease may be carried into new localities on the seed. A little con- 

 sideration will show that surface soil contaminated with the spores may readily be 

 blown on to the seed pods, and then get on to the seed during the threshing of the pods. 



Control. 



Great care should be taken to avoid the introduction of the disease into localities 

 where at present it does not occur. Seed should, if possible, be obtained from a source 

 known to be free from the disease. If seedlings are purchased they should oe care- 

 fully examined before planting, and if any infected plants are found, not only should 

 these be destroyed, but it would be well to discard them all, since the adhering soil 

 may contain spores enough to contaminate healthy ground. The spores are said to 

 resist the digestive juices of animals and, if diseased plants are fed to*stock without 

 being cooked, the manure is likely to prove a prolific source of new infections. The 

 spores set free in the soil may retain their vitality from three to seven years so that a 

 rotation which brings a cruciferous crop on the land not more than once in that time 

 may be necessary. The destruction of weeds is important since a number of these may 

 become infected and harbour the disease from year to year. Where the disease has 

 become established, applications of lime every few years arc of great value in dimin- 

 ishing the severity of the attacks. These should be at the rate of two to three tons 

 per acre and made some little time, preferably a year or eighteen months, before thf 

 sowing or planting of the cruciferous crop. 



