No. 4.] FUNGOUS DISEASES. 85 



a siuo-le one of which would fill a bushel-basket. Between 

 these two extremes is a host of fungous forms, numbering 

 over forty thousand species and presenting the most astonish- 

 ing variety and beauty of form, though in microscopic pro- 

 portions. All of these species, of whatever size or form, 

 are characterized by the fact that they can live only upon 

 organic matter, and that they are reproduced by means of 

 minute bodies of simple structure, called spores. What the 

 spores of fungi lack in size they make up in quantity. The 

 number of spores contained within a small puff-ball, and 

 issuing in the form of an imjmlpable dust, is almost incredi- 

 ble. The same is true of the familiar fungus producing 

 " smut " on corn ; the top of a pen knife dipped into this 

 black mass will come away loaded with over one million 

 spores. 



With the aid of a good microscope we can see how a 

 fungous spore germinates and to what it gives rise. If 

 spores of the common bread-mold be placed under conditions 

 suitable to their development, they each produce at one point 

 on the surface a delicate transparent tube, which grows 

 rapidly, branches profusely, and soon overruns and permeates 

 the substance upon which the spores have been sown. Some- 

 times, as in the case of the larger fungi, these minute tubes 

 are produced so luxuriantly that they form wdiite strands, 

 visible to the naked eye. Such is the "spawn" familiar to 

 growers of mushrooms. In the case of the parasitic fungi, 

 however, these tubes are seldom visible, both by reason of 

 their minute size and the fact that they are usually buried in 

 the substance of the fruit, leaf or stem upon which the fun- 

 gus is growing. 



Sooner or later, sometimes in the course of a few hours 

 after the germination of the spore, these vegetative threads 

 send up erect branches to the surface, and on the tips of these 

 branches a fresh crop of spores is produced. These fall off 

 readily, are swept up by currents of air or water, or are 

 carried by birds or insects to neighboring plants ; there they 

 germinate, and the process is repeated so long as the condi- 

 tions are favorable. Often as many as ten generations of 

 spores may thus l^e produced in a single summer ; and when 

 we consider the vast number of spores represented by each 



