148 



Elementary Principles of Agriculture 



217. How Fungi 

 Propagate. Fungi prop- 

 agate by minute cells, 

 called spores. They cor- 

 respond to seeds of 

 higher plants. They 

 require the same con- 

 ditions for germina- 



Fig. 89. Germinating spores of the potato tlon as Seeds. Fig. 89 

 blight fungus. Cross section through a Urmira Q " " 



portion of a stalk. Two germinating bilOWb d, 



^r^ 

 Spore 



, , ui- u+ 

 pOtatO 



spores (a, 6) piercing the epidermis, and 

 the threads penetrating the cells of the 



ing on a leaf. The first 



thread soon enters the plant and absorbs the moisture 

 and food substance of the potato leaf. It soon forms a 

 crop of spores, sometimes in only a few days. These 

 spores are blown to other 

 plants, and soon a whole 

 field will be blighted by the 

 fungus. Most species of fungi 

 grow on only one kind of 

 plant. The fungus that 

 causes grape mildew (Fig. 

 90) does not grow on any 

 other kind of plants but 

 grapes. The fungus that 

 causes the blasting of the 

 ears and tassels of corn 

 (corn smut) grows only on 

 corn. The fungus that causes 

 the smut of oats never at- 



tacks COrn. However, the 



, ., 



fungUS that produces the 



, , 



On grains alSO attacks 



Fig. 90. Downy mildew of grape 

 (Plasmopora viticola), showing 

 tuft of gonidiophores bearing 

 gonidia, also intercellular myce- 

 Ih 



lium. After Millardet. 



