5O FIRST REPORT ON ECONOMIC BIOLOGY. 



forming homogeneous masses of protoplasm, which possess the power 

 of creeping about by pushing out arm-like processes. The outer por- 

 tion of the plasmodia is of a thinner and more slime-like nature than 

 the inner portion, and this former is often left behind in the form of a 

 slime as the fungus progresses. 



The disease attacks turnips, swedes, and all cruciferous plants, 

 such as cabbage, radishes, wallflowers, candy-tuft, charlock, shep- 

 herd 's-purse, garlic mustard, and other weeds belonging to the 

 Cruciferae, and it would seem that wet and sticky soils are particularly 

 favourable to this fungus. 



The roots are attacked by the spores present in the soil entering 

 the living cells of the host plant ; these develop and form a slimy 

 mass of protoplasm, or plasmodium, which slowly makes its way from 

 cell to cell, eating up the contents, and giving rise to decomposition. 

 Roots so attacked are characterized by swellings of varying sizes and 

 shapes. If a section is made of one of these, it will be noticed, on 

 viewing the same under the microscope with a low power lens, that 

 there is an irregular, though somewhat ring-like, mottled area, and 

 examined under a high power lens, this is seen to be due to the 

 presence of a slimy mass of a stringy nature, wholly or partly filling 

 the cells. It will be further noticed that all the diseased cells are con- 

 siderably distended, although yet remaining intact. Such is the 

 appearance about the month of July. If the further changes were 

 watched, it would be noticed later that the slimy mass of protoplasm 

 becomes broken up into millions of exceeding minute, spherical spores, 

 each of which possesses a cell wall. 



The cells of the turnip are still intact, although considerably 

 more distended, and here the spores remain throughout the winter, 

 germinating, as already described, in the spring. As the roots decom- 

 pose the spores are liberated into the soil, and ready to infect a new 

 crop. 



Numerous experiments have been made as to the effect of lime 

 upon this disease, the most interesting and successful, perhaps, being 

 those carried out under the direction of Professor Gilchrist, at Cockle 

 Park Farm, Northumberland. 1 



Whilst no cure has been found at Cockle Park, it has been clearly 



1 " Report on Back House Rotation Experiments, and Finger and Toe Disease," by Prof. 

 Douglas A. Gilchrist. 



