44 MASSACHUSETTS HORTICULTURAL SOCIETY. 



plants that cases of the absence of chlorophyll become numerous, 

 and there, indeed, they include a majority of the species. These- 

 simple plants, without distinction of root, stem, and leaf, and 

 whose tissues contain no chlorophyll, are known collectively a» 

 Fungi. They vary greatly in size, structure, and development, 

 but they agree in these two particulars. Whence comes the food- 

 supply of these plants unable to provide their own? 



The dodder, as is well known, twines about the stem of some 

 green plant, and sends into its tissues absorbing organs, which 

 abstract its nourishing juices for the support of the dodder. 

 Here we have a typical example of the relations between the 

 parasite which thrives at the expense of its host, which is greatly 

 weakened or finally killed. The Indian pipe, on the other hand, 

 probabl}' draws its nourishment chiefly from the humus in which i4 

 grows, which is composed of decayed plant remains and contains 

 much organic matter still directly available. This plant is a type 

 of those called saprophytic. On the same basis of division the 

 fungi fall into two classes — those which live at the expense of other 

 living organisms, the parasites, and those which live on the 

 remains of dead organisms, the saprophytes. The latter conse- 

 quently cannot cause diseases, and may be passed over with the 

 remark that the best known saprophj'tic fungi are the toadstools. 



The attacks of a parasite on its host-plant cause a weakening 

 of its vitality, often produce also an abnormal stimulation which 

 results in the development of monstrous or distorted organs, and 

 frequently, finally lead to its death. The parasitic fungi, then, are 

 those which cause diseases of plants, and which have special eco- 

 nomic interest ; and among them are included the organisms which 

 cause diseases variously known as rots, moulds and mildews, namely 

 the members of the genus Peronospora, the mildeivs in the restricted 

 sense in which I have used the word. The mildews are parasites 

 chiefly of herbaceous plants, though they sometimes live on the 

 herbaceous parts of woody plants, and appear to the naked eye as 

 whitish, gray or brown, downy or felted growths on the under sur- 

 faces of leaves and sometimes on stems. Those parts of the plant 

 which are most directly affected are usually of a yellow or brownish 

 color, and this discoloration often appears before the fungus itself is 

 evident, affording to the practised eye the first indication of the dis- 

 ease. As we trace the life history of the mildew, it will perhaps be 

 an aid in presenting the subject, if we select a typical example and 



