1 36 MORPHOLOG Y. 



Promycelium bears four sterigmata and four gonidia (or spo- 

 ridia), which in favorable conditions pass back to the bar- 

 berry, germinate, the tube enters between cells into the 

 intercellular spaces of the host to produce the cluster cup 

 again, and thus the life cycle is completed. 



298. Higher fungi divided into two series. Of the higher fungi there 

 are two large series. One of these is represented by the mushrooms, a good 

 example of which is the common mushroom (Agaricus campestris). 

 (For the study of the mushrooms see Part III, Ecology.) 

 The large group of fungi to which the mushroom belongs is called the 

 basidiomycetes because in all of them a structure resembling a club, or basid- 

 ium, is present, and bears a limited number of spores, usually four, though 

 in some genera the number is variable. Some place the rusts (uredineae) in 

 the same series (basidium series) because of the short promycelium, and 

 four sporidia developed from each cell of the teleutospore. 



Sac Fungi. 



299. The other large series of the higher fungi may be rep- 

 resented by what are popularly called the "powdery mildews." 

 Fig. 164 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. 



300. Fruit bodies of the willow mildew. On this same 

 mycelium there appear later numerous black specks scattered 

 over the affected places of the leaf. These are the fruit bodies 

 (perithecia). 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 perilhecium. 



