EXPERIMENT STATION BULLETINS. 



489 



no food for itself but wliicli steals its living from another 

 plant. If a diseased spot is examined with a microscope, 

 the leaf tissue is found to be pierced by minute threads. 

 These threads are the body of the fungous parasite. After 

 the threads have grown in the leaf and occupied considerable 

 area, small black dots appear on both the upper and lower 

 surfaces. (Fig. 3.) 



The small black . dots are hollow spherical cases Needie- 

 which contain countless long needle-shaped bodies called Sht^^"''®^ 

 spores. (Fig. 4.) These spores are to the fungus what '^fi^^' 

 seeds are to the higher plants. A spore washed to a tomato parasitic 

 leaf and given favorable temperature and moisture will ^°^^- 



Fig. 4. Tliin section of spore case, sliowing long needle-sliaped spores. Magnified 800 times. 



sprout and enter the leaf, quite as a seed sprouts and grows, 

 only the soil the fungus uses is the leaf tissue. 



The spores of this fungus have a jelly-like coat and when 

 a diseased leaf is wet, the spores swell and push out of the 

 spore cases in sticky masses. When the spores are once out- 

 side the spore case they float apart in the water on the leaf 

 and frequently sprout and enter, thus making the spot larger 



The spores 

 float about 

 on wet 

 leaves, or. 



or causing new ones. 



The spores from a diseased leaf may be washed or splashed 

 from leaf to leaf during rains, or if the plants are worked 

 when wet, may be carried from plant to plant on the culti- 

 vator or on the clothes of tlie worker. 



Tlie s])ores can endure at least three days drying, hence, 

 lliose which wash to the ground may be dried on the dust 

 and blown about, thus leading to a wider distribution of the 

 disease in the field or from field to field. 



Rains splash 

 the spores 

 about. 



Cultivating 

 wet plants 

 spreads the 

 spores from 

 plant to 

 plant. 



