CHAPTER XXI. 



THE HIGHER FUNGI. 



411. The series of the higher fungi. Of these there are two 

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

 the other by the mushrooms, a good example of which is the 

 common mushroom (Agaricus campestris). 



Sac Fungi (Ascomycetes). 



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

 dews"; examples, uncinula, microsphaera, 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 mycelium lives on the 

 outer surface of the leaf, but sends short haustoria into the epi- 

 dermal cells. 



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

 lium 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 body, 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 

 uncinula, This rounded body is the perithecium. 



