ACOTYLEDONS LICHENS DIAGRAM 18. 



213 



There are many kinds of fungi similar 

 to mould, but still smaller, which are in- 

 visible to the naked eye, and can only 

 be detected by their ravages. The oidium 

 which attacks the vine is a fungus of this 

 description ; and the disease called mus- 

 cardine, which attacks silkworms, is 

 caused by another ; the potato disease is 

 either caused, or frequently accompanied 

 by, a similar fungus ; another produces a 

 disease called fumagine in the olive ; and 

 yet others produce mildew, smut, and ergot, 

 in cereals. The ergot chiefly attacks rye, 

 when, instead of the ordinary grain, we 

 see large black horny grains developed, 

 shaped something like a cock's spur. 

 Ergot is poisonous, but is of great use in 

 medicine. Man himself is subject to 

 diseases caused by the presence of fungi 

 of this kind, such as the thrush and Erg,t of %e. 



ringworm. In the thrush, the white points which form on the 

 tongue and inside the mouth of children, are caused by the pre- 

 sence of a fungus. In the ringworm, it is also a fungus which 

 form the yellow crusts shaped like buttons, hollow in the middle, 

 which grow at the roots of the hair. 



We may add that the yeast which we have mentioned as found 

 in beer vats is also a fungus of this kind. 



FAMILY OF LICHENS. 



The Lichens resemble fungi, but instead of being moist, like the 

 latter, are dry. They often resemble parchment, and we should 

 scarcely take them for living plants if we did not see them grow 



