CHAPTER XXI. 



THE HIGHER FUNGI, 



411. The series of the higher fungi. — ()i these there are two 

 large series. One of these is represented by the sac fungi, and 

 the other by the mushrooms, a good e.xample of which is the 

 common mushroom (Agaricus campestris). 



Sac Fungi (Ascomycetes). 



412. The sac fungi may be represented by the "powdery mil- 

 dews"; e.xamples, uncinula, microsph;era, podosphaera, etc. 

 Fig. 225 is from a photograph of two willow leaves affected by 

 one of these mildews. The leaves are first partly covered with a 

 whitish growth of mycelium, and numerous chains of colorless 

 gonidia are borne on short erect threads. The masses of gonidia 

 give the leaf a powdery appearance. The mvcelium lives on the 

 outer surface of the leaf, l;ut sends short haustoria into the epi- 

 dermal cells. 



413. Fruit bodies of the willow mildew. — On this same myce- 

 hum there appear later numerous black specks scattered over 

 the affected places of the leaf. These are the fruit bodies (per- 

 ithecia). If we scrape some of these from the leaf, and mount 

 them in water for microscopic examination, we shall be able to 

 see their structure. Examining these first with a low power of 

 the microscope, each one is seen to be a rounded fjodv, from 

 which radiate numerous filaments, the appendages. Each one 

 of these appendages is coiled at the end into the form of a little 

 hook. Because of these hooked appendages this genus is called 

 tincimda. This rounded bodv is the perithelium. 



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