312 Wisconsin State Horticultural Society. 



consequently they can only flourish on the plants which produce 

 these substances. This is a matter of inference rather than obser- 

 vation ; for we do not yet know, for example, what the chemical 

 substance is which enables the fungus known as Spkceria morbosa 

 to grow on plums, and some varieties of cherries, and produce on 

 them the excrescence known as " black knot,'' while it will not 

 grow on apples or pears. The limitation of different species of 

 fungi to a single plant, or at least to a comparatively few plants, 

 is a great protection to the farmer; for, were this not the case, a 

 disease once attacking a single crop would cause a general devas- 

 tation. 



Not only are fungi destitute of the green coloring matter found 

 in the greater part of other plants, but their structure is much 

 more simple than that of the ordinary plants with which you are 

 most familiar. Instead of being composed of a more or less solid 

 mass of cells packed together, as are the bricks in a house, for a 

 great part of their existence fungi are composed only of delicate, 

 colorless threads. When we say delicate, we must understand 

 that the word refers to the general appearance of the threads and 

 not to a lack of resisting power. If we submit the cells of the 

 higher plants and the threads of fungi to the action of chemical 

 reagents, as caustic potash or acids, we shall find that the threads 

 are less quickly destroyed than the cells: consequently if we 

 have a leaf in which a fungus is growing, we are able, on boiling 

 it in caustic potash, to cause a separation and disintegration of the 

 leaf-cells, while the threads of the fungus remain comparatively 

 unaffected. The name given to the threads of the fungus taken 

 collectively is Mycelium : and the separate threads are called 

 hyphcB, or flocci. In the case of the moulds which do not grow 

 upon living plants, the mycelium forms usually a mass looking 

 more or less like cotton wool. In those which inhabit living 

 plants, the threads wind about amongst the cells of the plants on 

 which they are growing, and, when seen on the surface, appear 

 like a fine web or frost work. 



As has just been remarked, for a great part of their existence 

 fungi consist of a mass of threads, but, under favorable circum- 

 stances, reproductive bodies known as " spores " are produced, 



