280 COLLEGE BOTANY 



green molds which are found on leather, fruits, vegetables, cheese 

 and other organic materials. They produce an abundance of 

 mycelium and numerous conidia, which are arranged in chains 

 which radiate from a common origin. The sexual reproduction 

 is by means of antheridia and oogonia. Fertilization is followed 

 by the formation of an ascocarp' bearing eight-spored asci. 



The gemisPenicilUum (Fig. 129) contains numerous species 

 of blue molds which are found growing on fruits, vegetables, 

 cheese, bread, leather and other organic materials. Some of them 

 are very important as the causes of decay in fruits, especially 

 oranges and lemons, while others are used for the development 



Fig. 129. — Penicillium. 



of desirable flavors in cheese. Their reproduction is very similar 

 to that of the Aspergillus. 



The genus Microsphoera (Fig. 130) is a good type of the 

 powdery mildews which are parasitic on many of the higher 

 plants. They live on the surface of the leaves and are held in 

 place by small haustoria which penetrate the epidermal cells. 

 These surface mycelia give rise to erect sporophores bearing 

 single terminal chains of conidia. The oogonia and antheridia 

 are uninucleate terminal cells. Fertilization occurs in the usual 

 manner and a solitary ascocarp- is formed. The ascocarps of the 

 various genera of the powdery mildews present well-defined char- 

 acters. One of the most common is M. alni, which causes the 

 well-known whitish growth on the leaves of the lilac and many 

 other plants in the late summer and fall. Some of the powdery 

 mildews are very destructive to our agricultural crops. 



The Pezizas (Fig. 131) are cup-shaped and frequently very 



