Minnesota Plant Diseases. 



307 



great numbers. These spores are small, oval, or cylindrical, 

 colorless cells. Their production is accompanied by the secre- 

 tion of a sugary fluid known as "honey dew," which is at- 

 tractive to insects. The latter in their search for the "honey 

 dew" distribute the summer spores from plant to plant and 

 rapidly spread the disease. Toward the end of the summer, 

 the formation of summer spores ceases and the underlying fun- 

 gus mass becomes more compact and hard, and the external 



threads form several layers of 

 cells which contain a very 

 dark purple coloring matter. 

 This fungus mass is now 

 known as the sclerotium and 

 is the ergot of commerce. 

 The form of the ergot varies 

 in the different grasses. The 

 ergot of rye (commercial er- 

 got) is long and cylindrical 

 and slightly curved. The er- 

 got of wheat is much shorter 

 and thicker, while the ergot 

 of wild rice is still shorter and 

 roughly egg-shaped. The er- 

 got is a storage organ and 

 usually rests through the win- 

 ter. The storage material is 

 a kind of starch, known as 

 fungus starch, which is stored 

 up in the cells. The fungus 



Fig. 154.— The ergot fungus (Claviceps pur- tlircads are SO COmpactcd tO- 

 purea), on rye. The large f.ngus stor- ^ ^ j ^^^^ ^ ^^^^ 



age organ (sclerotium or ergot) is seen b^'-^' -' ^ ^ -' 



near the top of the head. After Clinton, of cclls vcry similar in appear- 

 ance to that of the pith of some flowering plants. The ergot 

 rests in or on the ground, where it is often sown with the grain, 

 until early summer. Under the proper conditions of moisture 

 it then develops further. From the surface of the ergot arise 

 several short, violet-colored stalks, which bear at their tips yel- 

 lowish spherical heads. The latter are the spore-sac-capsule 

 cushions, as may be seen by the small protruding necks of the 



