67 



Storage of the food materials manufactured in the leaves. 

 The reserve supplies are thus tapped by the fungus, with 

 the result that the quantity of sugar stored by the grow- 

 ing root rapidly diminishes. In such instances many of 

 the cells of the root are enormously enlarged and differs 

 as regards their contents from those of a healthy root. 



The healthy cells are lined by the colourless, jelly-like, 

 living protoplasm with its nucleus and contain cell-sap rich 

 in sugar. Diseased cells differ from these in several re- 

 spects. They are generally much larger; protoplasm is 

 present as before, but it looks frothy and in it can be seen 

 granular masses of other slimy substance which is the 

 protoplasm of the fungus slowly absorbing that of its 

 victim. It is a remarkable fact that the early effect of the 

 parasite upon the cell is to stimulate it to enlarge and 

 even to divide, and thus obtain more food material from 

 the adjoining cells, and this is ultimately used by the 

 unbidden guest. Gradually the protoplasm of the fungus 

 increases in size until the whole of the protoplasm of the 

 cell disappears. Then the fungus undergoes certain 

 changes and soon the cell is seen to be filled with a large 

 number of tiny round bodies. These are the spores of the 

 fungus, and as they only measure one fifteen thousandth 

 of an inch in diameter they can only be seen when very 

 highly magnified. A single diseased cell w^ill contain at 

 least 100,000 of these spores, and since the diseased part of 

 a turnip, for example, contains many thousands of such 

 cells it is. easy to see that in one such root millions of the 

 spores of the fung-us are produced. 



If a very small piece of a diseased root is broken up in 

 water myriads of the spores are liberated from the cells. 

 After a few^ hours very remarkable changes can be observed 

 to take place in these. Each tinv spore swells somewhat 

 and then bursts producing a small hole in one side of the 

 colourless membrane. Gradually the living protoplasm 

 within squeezes its way through the aperture thus formed. 

 As soon as it is free it begins to wriggle and move about 

 as a minute speck of living protoplasm. The protoplasm 

 at one end is drawn out into a fine hair, and the 

 lashing of the w^ater by this hair causes the movement of 

 the minute organism. After a time the movements of 

 these specks of protoplasm become more sluggish and soon 

 they only creep about by slow movements, first pushing 

 one part of the protoplasm forward and dragging the 



