Minnesota Plant Diseases. 9 



from the flower-pot algae, the green felts and the pond scums, 

 and possibly from the red sea-weeds. 



The fungi therefore comprise low forms of plant life which 

 have descended from algal stock and which by a change in their 

 nutritive methods have lost their leaf-green and have come to 

 possess a vegetative mechanism, composed of more or less 

 branched threads known as a mycelium. 



The number of fungi in Minnesota is undoubtedly very 

 large. It has been estimated at between 2,500 and 3,000, out 

 of a total number of 7,000 Minnesota plants. The minute size of 

 many of these fungi, — some of the entire plants cannot be seen 

 without the aid of a hand-lens, — the difficulty of observation, 

 the great resemblances of forms and the complex methods of 

 life make the determination of these plants a slow task, and the 

 exact number of Minnesota fungi will probably not be known 

 for some years. The rate of constant additions of new forms is 

 sufficient indication of the very large number which exists in 

 the state and points towards a confirmation of the above esti- 

 mate. 



The fungus method of obtaining nutrition. It was stated 

 above that fungi had lost the leaf-green of their algal ancestors 

 and were therefore unable to make starch from water, soil and 

 air constituents but compelled to derive their elaborated food 

 from other sources. Two methods have been adopted. In one 

 the fungus derives its nutritive material directly from living 

 plants. Such are parasites, and the plants upon which they 

 feed are known as host plants. In the other method the fungus 

 derives its prepared food from the dead products or remains of 

 animals or plants, as leaf-mold, bread, preserves, etc. Such 

 plants are known as saprophytes. In both of these cases the 

 food obtained is at least partially prepared. 



How the nutritive method is expressed in structure. It is a 

 law which covers all living things, plants as well as animals, 

 that the complexity of the structure of an organism depends on 

 the amount and kinds of work which it can perform. When 

 an organism has its food prepared by no effort of its own, it 

 soon shows the loss of power to do that work. This loss of 

 power is usually expressed in loss of certain structures, or in 

 the simplifying of such structures. Such an effect is commonly 



