426 INSECTS AFFECTING VEGETATION 



and that the names applied will vary accordingly. The names are 

 not simply blight, rust, etc., indiscriminately applied they are given 

 with reference both to the parasite and its effect on the host plant. 



Parasitic fungi and bacteria which cause disease, being plants, 

 though of lower class, have differences among themselves which may 

 be clearly designated and defined. The names applied to them are 

 accompanied by specific and generic descriptions which mark off 

 the sort as definitely as do the descriptions on higher plants such as 

 ferns, flowering plants and trees. The extreme minuteness of the 

 parts of parasitic fungi and bacteria make necessary the use of the 

 microscope in their description and detection. The parts called spores 

 which reproduce these minute plants have special form, size, etc., 

 by which these are recognized when found. 



The agencies for the spread of parasitic diseases are those oper- 

 ations in which w r e engage or those which surround and envelop the 

 plants as well as ourselves. Light spores will be carried by currents 

 of air like particles of dust. All spores or germs of these lower plants 

 may be carried by numerous agencies such as insects, higher ani- 

 mals, and man. They will also find entrance into plants by what- 

 ever openings exist at the time. The epidermis of a green leaf or 

 stem has breathing pores or stomates in it; the leaves of mustard 

 plants have water pores in them and wounded plants have, those 

 fresh openings to invite the entrance of the disease conveying spores 

 or germs. 



The remedies for plant diseases are based upon the character and 

 life history of the particular parasitic growth with which we have to 

 deal and upon the nature of the host plant itself some hosts being 

 very different from others in respect to permitting of sprays of fungi- 

 cides or insecticides. Common sense inferences are always of use in 

 dealing with plant diseases. If the soil is too wet, drain it; if late 

 growth predisposes to winter injury, avoid such growth; if over- 

 bearing weakens plants, prevent it by thinning the fruit. 



The philosophy of seed treatments is stated under diseases 

 which infest the seed ; that of soil treatments or disinfection, under 

 soil infesting disease, and the general doctrines of sprays, fungicides, 

 etc., under that heading further on. The progress made in plant dis- 

 ease prevention throughout the world during the period of about 26 

 years which has elapsed since the discovery of Bordeaux mixture in 

 France shows how well adapted that discovery was to the needs 

 of the times. 



The progress made in recent years in the study and control of 

 plant diseases has been made possible by the agencies recently de- 

 veloped in the United States and Canada in the Agricultural Col- 

 leges, the Agricultural Experiment Stations, and the Departments of 

 Agriculture. It is not expected that this advance in our knowledge 

 of the disease of plants or of the methods of disease control will soon 

 wane. Efforts like the present one to present briefly the doctrines 

 of disease and the philosophy of disease control together with brief 

 descriptions of prevailing diseases in our state, have for their pur- 

 pose the wider dissemination of the body of present day knowledge 



