1890.] PUBLIC DOCUMENT — No. 33. 19D 



consists of organic substances, it is evident that it must come 

 from one of two sources ; either from living organisms, 

 animal or vegetable, or from dead organisms in a more or 

 less advanced state of decomposition. Among flowering 

 plants there are a few which are thus dependent, the best 

 known of which are the white " Indian pipe" (Monotropa) 

 of our woods, and the "Dodder," which twines its yellow 

 or orano-e- colored leafless stems about our ffolden-rods and 

 similar plants. But nearly all of the chlorophyll-less plants 

 are of much simpler structure. They are mostly very 

 small, and show no distinction of separate organs, like the 

 stem and leaf of higher plants. 



These simple plants may best be grouped under three 

 heads, the true Fungi, the Bacteria, and the 8lime Moulds. 

 Many of them live on decaying organic matter, the remains 

 of dead organisms of various sorts, and are known as sapro- 

 phytes, or corpse-plants. Others, on the contrary, resemble 

 the dodder in drawing their nourishment directly from living 

 plants or animals, on which they are said to be parasites. 

 The plant or animal at whose expense the parasite lives is 

 called its host. It is this latter class of plants which has 

 special interest to all who cultivate the higher plants, since 

 its members cause the numerous and frequent plant diseases 

 ordinarily known as fungous diseases. As we have seen, 

 they attack their host plants for the purpose of obtaining 

 the organic food supply necessary to their growth, which 

 they are unable, from lack of chlorophyll, to provide for 

 themselves. 



The efiects of diS*erent parasites on their host plants vary 

 greatly. It is evident that the host plant must always be 

 weakened by being robbed of a part of its food ; but the 

 amount taken seems, in some cases, to be insignificant, so 

 that no serious damage results. On the other hand, the 

 destruction of the host is sometimes so rapid and so com- 

 plete that there can be no doubt that the parasite exercises 

 a more positively fatal influence than merely that of turning 

 the food supply of the plant from its proper channels. 

 Between these extremes one may observe all degrees of 

 harmfulness on the part of the various parasites ; and the 

 harm done by any particular one may vary widely in 



