2 20 TRANSACTIOXS OF THE ILLINOIS 



The conditions and places where fungi may be found growing are 

 many; as on or in the ground, upon or in decaying animal or vegetable 

 substances, or as parasites upon or within the tissues of living plants or 

 animals. To the first belong mushrooms, toadstools, puff-balls, etc., while 

 mildew on grapes may be mentioned as a parasite on the outside of a plant. 

 Of parasites within plants the one that causes potato rot, rust on black- 

 berry leaves, and the one we have under consideration, are good examples. 



While the reproductive organs or spore-cases of fungi live only a 

 short time, the mycelium, or meshes from which these organs arise, may 

 lie dormant for days or even years until proper conditions for further 

 development shall reinvigorate it. As, for example, who has not seen the 

 dry, brown knots that distort the twigs of our red-cedar trees send forth 

 their mass of orange-colored reproductive organs during a rainy day, dry 

 up again as the clouds are replaced by sunshine, and repeat this process 

 year after year, the number of knots increasing as the new spores find 

 suitable places for development on other twigs. 



A brief description of the life-history of the fungus-producing potato 

 rot {^Peronospora infestans) may perhaps best illustrate that which pro- 

 duces dry rot in apples. In the pptato fungus the spore falls, we may 

 suppose, upon the stalk of the growing plant. If there is sufficient moisture 

 for its development it sends out its prothallus, or what we may call its 

 rootlets, which penetrate the cells of the epidermis until they reach the 

 intercellular passages in the interior. Here fertilization takes place, after 

 which it sends out its mycelium to all parts of the plant. Spore-cases are 

 developed on the leaves and sometimes on the tubers, but the mycelium 

 in the tubers, unless the surface is broken, may remain dormant till the 

 following season; or the development may be more vigorous and the whole 

 plant succumb to the exhaustive growth of the parasite. 



I have not had the time to trace the life-history of the apple-rot 

 fungus, nor have I seen that history as traced by any one else ; but from 

 what I have seen I think there is a close analogy between that history and 

 the one just given. As, for instance, we know that when a tree once 

 becomes infected that in successive years it produces apples that at a 

 certain season begin to decay and in the rotting places show unmistakable 

 evidences of the presence of fungus. From this we may suppose that the 

 mycelium permeates the whole tree, living dormant from one year to 

 another, and sending forth the organs of reproduction from the apples as 

 they reach a certain stage of growth. As the disease spreads from the 

 infected tree to those in its immediate vicinity, it is quite probable that 

 the spores fall on the apples, or possibly on the green leaves of the adjoin- 

 ing tree, and grow in a manner similar to the spores of the potato fungus. 

 If this be true, not only the apple but the whole tree would be infected. 

 Like the potato rot, certain varieties are more susceptible to the influence 

 of the disease than others ; and the reason seems to be that they present 

 a surface better adapted to the development of the spores than others. 



On the subject of remedies I can say but little, and that mostly of a 

 negative character. If my theory of the life-history of the fungus be 

 correct, then I know of no remedy that does not involve the destruction 



