THE PROTOZOA THE DAWN OF LIFE 13 



years causes very serious loss to the agriculturist, is Plasmodio- 

 phora brassica, which attacks the turnip and cabbage crops, pro- 

 ducing the disease popularly known as " Fingers and Toes," 

 " Anbury," or " Club-root." The name Plasmodiophora has 

 reference to the slime-like character of the organism, and its re- 

 semblance to the so-called " Slime-fungi," or Myxomycetes, which 

 are now generally included as Protista. 



The roots of cabbages, turnips, cauliflowers, and other allied 

 plants are frequently to be seen greatly distorted and deformed 

 by swellings of varying size and shape, the result of the presence 

 of Plasmodiophora in the root-tissues, while the plants present 

 a miserable, stunted, starved appearance. If a carefully cut sec- 

 tion from one of these diseased root-swellings be examined under 

 the microscope, it will be seen that not only are the vascular 

 bundles or strands of woody tissue displaced and altered, but that 

 many of the cells of the tissues are enormously overgrown, and their 

 contents quite different from those of normal, healthy cells. 



Some of these giant cells will be seen to be filled with a semi- 

 translucent, granular, foamy mass of protoplasm, which undergoes 

 slow movements, while the embedded granules are constantly 

 changing their position. The cell is, in fact, tenanted by a plas- 

 modium 1 consisting of a translucent mass of protoplasm con- 

 taining water- vacuoles, oily drops, granules, etc. 



Other giant cells will be seen to be packed with minute, sphere- 

 shaped spores. These spores become scattered in the soil as the 

 diseased roots of the host-plant rot. Under suitable conditions of 

 temperature and moisture the spores swell, rupture, and tiny 

 protoplasmic organisms possessing a nucleus and a single flagellum 

 make their escape into the surrounding soil. These penetrate 

 into the roots of the seedling cabbages or turnips, probably gain- 

 ing entry by the root-hairs, in much the same way as the proto- 

 plasmic zoospores of Pythium, the fungus which causes " damp- 

 ing-off " of seedlings. Having obtained entry into the cells of the 

 root, the Amcebulae lose their flagella, soon increase in size, and 

 their nuclei divide. 



The tissues of their host once entered, the Amoebulae commence 

 a battle with the living protoplasm of the cells for possession, 



1 Plasmodium, Plasmodia derived from the same root as protoplasm, and 

 referring to the protoplasmic nature of the organism. 



