Horticulture. 



92 



Different causes were assigned for this disease. At first farmers thought that 

 tbe Disease was caused by some insect depositing its larvae in the root, which 

 produce a swelling which was then called a root gall, but this theory was eventually 

 discarded. Then it was generally accepted that the "clubbing" or swelling of the roots 

 was due to a degeneration of the plant affected, what was known as a "sporting" 

 condition when the plant reverted to a considerable extent to its original wild form. 

 But this theory would not apply to every case, as the disease was found sometimes 

 where the most approved system of cultivation had been adopted and observed 

 so as to prevent any degeneracy or reversion to an original type. To a Russian 

 Botanist, Woronin, Ave owe the discovery of the true cause of clubbing. In 1876 he 

 found out that the disease is due to a parasitic fungus belonging to the group of 

 Myxomycetes, or slime fungi, so called because they differ essentially from ordinary 

 fungi in consisting of a naked moving mass of protoplasm or cell matter technically 

 known as a Plasmodium, hence its discoverer gave it the name of " Plasmodvphora 

 brassicce." But let us remember it as club root. It is interesting and very useful 

 to know something of the nature and life history of this fungus, especially as it 

 will better enable us to take measures to prevent the disease- The jelly-like 

 substance or mass of protoplasm, which is a living substance, takes possession of 

 the root cells of the plant, makes its way from cell to cell absorbing the contents 

 of each cell and naturally feeding on the nourishment of the plant itself, and 

 causing the cells of the root to enlarge and present the clubdike appearance so 

 common in the disease. Subsequently this mass breaks up into a number of spores 

 which are all reproductive bodies, on which the propagation of the fungus depends, 

 and which spores are let out into the soil in myriads on the decaying of the root 

 in which they have been contained to germinate in the next crop sown. These 

 spores want moisture for their germination, which when present enables the 

 contents to burst through, leaving the seed case behind. The living spore is able 

 to move about by means of a delicate threaddike piece called a "cilium" or hair, 

 and then gets the name of a "zoospore." Coming in contact with a tender root of 

 a suitable host plant or a plant on which it can feed, it finds its way inside most 

 probably through the root hairs, and there the process of enlargement at the 

 expense of the plant is repeated with its dire results. The Plasmodium or club root 

 fungus tlmves on the food of its host plant. It is a real parasite and in the end 

 kills its host. All parasitic fungi live at the expanse of certain other plants which 

 are known as host plants, and it is important to recognise the host plants of this 

 parasite, as we could by keeping a garden clear of the host plants which are weeds 

 and of no use to us but are needful for the support of this parasite, in a great way 

 prevent the spread of this disease. As far as is known, this fungus only attacks or 

 uses as its host, plants belonging to the Natural Order Cruciferte, such as cabbage, 

 cauliflower and knol-khol among cultivated plants, and the shepherd's purse and 

 hedge mustard among the common garden weeds. 



It only remains for us now to see what remedies have been suggested and 

 could be offered for the prevention and cure for this disease. 



(1.) From the easy manner in which the spores are propagated it is but 

 evident that the first preventative is to get rid of all diseased plants, a source of 

 future infection. The diseased stumps of infected plants should never be left to rot 

 in the soil or be ploughed or turned into the soil as manure, or added to the manure 

 heap, but should be removed and burnt, or at least taken away as far as possible 

 from the garden. 



(2.) We should starve out the fungus by not giving it its host plants to feed 

 on. On a plot of ground affected by the disease alternate crops should be tried and 

 plants introduced on which the fungus does not grow, such as potatoes, beans, lettuce, 

 peas, etc., and on a plot on which the disease has been very severe it ie beet to plant 

 grops other than cruciferous for two or more seasons. 



