DISEASES OF PLANTS. 



70 



equivalent of the roots and leaves of a flowering plant ; that is, 

 it is that part of the fungus which takes in food, and when a 

 sufficient quantity of food has been accumulated, the mushroom 

 is produced on the surface of the bed. The mushroom, as 

 commonly understood, is not the entire fungus, but only its fruit, 

 which appears at the surface of the bed for the purpose of 

 enabling its seeds or spores as they are called, to be distributed 

 by wind or other agents. In like manner the mycelium of 

 parasitic fungi is present in the tissues of the living plants on 

 which they grow, long before the fruit of the fungus appears on 

 the surface. As a matter of fact, when the fungus appears on the 

 surface of the plant it represents the last stage of the disease 

 and not the first ; the injury has been done ; the mycelium has 

 been absorbing the food prepared by the plant for its own use, 

 the plant-cells are destroyed by the mycelium, and the fruit of 

 the fungus appears on the surface of the diseased plant for the 

 purpose of being carried by wind, insects, or spraying, on to the 

 leaves of other healthy plants, where the same course of develop- 

 ment takes place. 



From the above account it will be seen how very necessary 

 it is to remove all traces of fungi that appear on living plants, 

 either by removing and burning the diseased parts, or when it 

 is not desirable to do this, then to spray or wash the affected 

 plants with some solution that will destroy all spores present. 

 If this method of promptly destroying all traces of fungi on 

 their first appearance is persistently carried out, there is but 

 little fear of an outbreak on a large scale, as it is quite as 

 impossible for fungi to appear in the absence of fungus spores as 

 it would be to expect a crop of peas to spring up without 

 having previously sown the seed necessary for producing the 

 same. The gardener should accustom himself to treat every 

 fungus, large or small, mildew or toadstool, in the same manner 

 that he treats weeds in a seed-bed, as something that may do a 

 great deal of injury, but which cannot possibly do any good. 

 The spores of fungi are exceedingly minute, and are readily 

 carried by currents of air, insects, birds, animals, &c, from one 

 place to another, and if such spores alight on the damp surface 

 of a leaf of the particular plant on which the fungus is parasitic, 

 the spore germinates at once, and within a very short time the 

 mycelium has pierced the skin of the leaf and entered the tissues, 



