66 



Seedling cabbages, which show by the nodular swell- 

 ings that they are attacked by Club-Root, are often 

 exposed for sale. Of course it is inadvisable to plant 

 such seedlings, for not only is it extremely unlikely that 

 they will produce healthy plants, but when they decay in 

 the ground they will infect the soil. If any plants of the 

 cabbage family are grow in the same soil within two or 

 three years of this infection, thev will almost certainly 

 suffer from the disease to an even greater extent. 



The disease with which we are dealing should not be 

 confused with the gall-like swellings on the roots of 

 cabbages and turnips, sometimes caused by the larva of a 

 beetle that lives within the cavity of the swollen tissue. 

 Eelworms, as well as certain bacteria, are also able to 

 produce small swellings on the roots of many plants, in- 

 cluding Crucifers. It is a little unfortunate that frequently 

 any swellings on roots of cruciferous plants are spoken of 

 as Club-Root without reference to the causal organism 

 Since, however, in the vast majority of such cases the slime 

 fungus, Plasmodiophora Brassicae, is the cause, I am re- 

 stricting the name Club-Root or Fingers-and-Toes to 

 the disease of which it is the cause. Whilst the life history 

 of Pythium and of the other fungi mentioned in the last 

 chapter is typical the Club-Root fungus differs somewhat 

 in life story and mode of nutrition. 



When one of the diseased roots, say of turnip, is cut 

 across and examined under a microscope it is found that 

 the tissues of the root are altogether abnormal, many of 

 the cells being strangely altered. In the healthv root of 

 the turnip we can distinguish an outer band of softer 

 tissues surrounding a central core containing a certain 

 number of woody elements arranged like the spokes of a 

 wheel. Between the last-named are broad wedges of 

 softer cells which are packed with the reserve food material 

 that is stored in the root of the turnip in the form of 

 sugar. The root increases in thickness by the growth and 

 division of a layer of cells near the outer part of the 

 central core. When attacked by the fungus of which we 

 are speaking, the whole machinery for the growth of the 

 root is, as it were, thrown out of gear; cells which normally 

 would produce woody tissue simD^ give rise to giant thin- 

 walled cells, and the result is an excessive production pf 

 thin- walled tissues. This also occurs in the position of 

 the tissues which normally serve for the conveyance and 



