1 1 14 General Notes. [Dec. 



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(Extracted from the American Naturalist, December, 1887.) 

 BOTANY.s 



Character of the Injuries produced by Parasitic Fungi 

 upon their Host-Plants. 6 — The first and most general injury 

 which is produced upon plants by parasitic fungi results in con- 

 sequence of the essential character of the fungus. Green plants 

 have the power of converting inorganic materials into food for 

 themselves. Fungi have not this power, but depend for their 

 food entirely upon materials that have been previously elaborated 

 by some green plant. Parasitic fungi take their food from their 

 host while it is yet alive. The consequence to the plant, there- 

 fore, is a loss of food, a withdrawal of formed nutritive material, 

 resulting, to greater or less extent, in starvation. In individual 

 cells the contents usually suffer the greater injury, but the wall 

 is also injured, as when penetrated by the haustoria, or suckers, — 

 e.g., upon the mycelium of Peronospora. But the special office of 

 the haustoria is to absorb nutriment from the cell-contents. In 

 some cases, as the above, the cell may live to be the continual 

 prey of the parasite, and in some cases the cell is killed. 



(2) While the food-supply of the plant is reduced, its power 

 to replenish it is at the same time impaired, — i.e., in case the 

 fungus grows upon the green parts, as it does most frequently. 

 The passage of light to the cells may be obstructed. The white 

 moulds, or mildews, must obstruct it to some extent, black moulds 

 growing over the surface, much* more. The latter may occur 

 either as true parasites, or as saprophytes upon " honey-dew." 



Impaired nutrition weakens the physiological power of the 

 chlorophyll. The life of the cells preyed upon is frequently 



5 Edited by Prof. Charles E. Bessey, Lincoln, Nebraska. 



6 Read before Section F, A. A. A. S., August, 1887. 



