INTRODUCTION 



The principal non-flowering vegetable parasites which cause 

 plant diseases belong to three divisions: the Slime Molds (Myxo- 

 mycetes); the Bacteria (Schizomycetes) ; and the True Fungi 

 (Eumycetes including the Phycomycetes). The term fungi, in 

 the broad sense, is often used to include all three of these divisions. 

 All are devoid of chlorophyll and therefore all differ from the green 

 plants in the essential ways which result from this deficiency. 

 Transpiration, respiration, and true assimilation are the same as 

 with the green plants, but photosynthesis or starch manufacture 

 cannot be accomphshed by them. SunUght being thus useless to 

 ■ them directly they can live in the dark as well as the light. Having 

 no ability to elaborate their own foods from inorganic matter 

 these organisms are limited to such nutriment as they can obtain 

 from plants or animals which have elaborated it; that is, they must 

 have organic foods for their sustenance. 



The fungi have acquired various food habits and adapted them- 

 selves to different methods of nutrition. Some are nearly om- 

 nivorous and can subsist upon almost any decaying tissue or upon 

 soils or solutions rich with organic debris. Others thrive only 

 upon special substances, as for example, some particular plant or 

 animal, the host, perhaps only upon some particular part of that 

 plant or animal. The organisms that prey upon living things are 

 called parasites. Those living upon dead things are sapro- 

 phytes. No hard and fast line can be drawn between these two 

 classes. An organism which is usually a saprophyte may Uve 

 upon a dead member of some plant, gradually encroach upon the 

 still living part and thus become partially a parasite. Again there 

 are times in the history of a plant when life ebbs so low that it is 

 diflScult to tell the living from the dead. The pulp of the apple 



I 



