198 Minnesota Plant Diseases. 



the fruiting bodies of puff-balls. In fact many of the fruiting 

 bodies resemble so closely the true puff-balls that botanists for- 

 merly classified them as such and the amateur is constantly de- 

 ceived by the resemblance when he first meets with these forms 

 In the field. When the fruiting body is formed the entire plas- 

 modium is used up in its construction and the spores are blown 

 about by the wind and thus disseminated. The slime molds 

 exhibit, therefore, a lowly method of animal life and a fungus- 

 like reproduction. The slime molds, living as plant-parasites, 

 live in the cells of the host plant and do not form fruiting bodies 

 like those of the true wood-dwelling saprophytes. One slime 

 mold parasite causes the club root of beets living in the cells of 

 the swollen portions. The slime-mold parasites of animals 

 cause various diseases. Malaria is due to a slime mold which 

 lives a part of its life in the body of the mosquito and is trans- 

 ferred to man in the bite of the insect. Texas fever of cattle 

 and several diseases of man are traceable to the action of organ- 

 isms of this slime-mold group. (Figs. 100, 179,180.) 



Other kinds of plants as disease-causing organisms. As has 

 already been stated, fungi constitute an overwhelming majority 

 of those plant diseases which are of plant origin. Besides these 

 and the bacterial diseases, a few are known which are caused 

 by other kinds of plants though they are with few exceptions of 

 slight economic importance. Only a short account of them will 

 be permissible in this work. 



Algae. A number of blue-green algae live as place parasites 

 in cavities and tissues of higher plants. Such are doubtless not 

 true parasites in their nutrition but their position in the tissues 

 of the host offers them protection of place and a safe harbor. 

 Such are found in floating water-ferns, and in the roots of 

 the greenhouse sago palms. 



Some flower-pot algae are also place parasites. The posses- 

 sion of leaf-green enables them to manufacture their own food. 

 A few such green algae are known on water-inhabiting seed 

 plants, e. g., several species of the tiny duck weed. No diseases 

 of economic importance are known in these groups. 



Mosses and fernworts and lower seed plants. No Minne- 

 sota members of these groups of plants or of their alliances are 

 known as parasites of other plants. Some of the latter groups 



