256 



GENERAL MORPHOLOGY OF PLANTS 



zation and germinate.* This ripening and functioning of eggs 

 without fertilization is known to occur in some animals, notably 

 the plant lice, and in some of the flowering plants. 



413. Stoppage of drain pipes by water molds. Some of the 

 water molds (notably Leptomitus lacteus) grow in waste pipes and 

 drains from refrigerators, cider presses, etc., and cause annoy- 

 ance by stopping the flow of the waste water. Flushing with 



water often clears the drain, 

 but if the fungus continues to 

 be troublesome its growth can 

 be prevented by flushing the 

 drain now and then with a 

 weak solution of blue vitriol. 



i 



The Downy Mildews and 

 White Rust. 



414. The downy mil- 

 dews. The downy mildews 

 received this name from the 

 numerous sporophores, often 

 branched, which are crowded 

 in spots on the parts of 

 plants which they attack. 

 These crowded sporophores 

 look like so much down, 

 and the affected areas have 



Fig 2is also a mildewed appearance. 



Downy mildew of grape (Pksmopora viticoia), They are true parasites, since 



showing tuft of gonidiophores bearing gonidia, also , i IT- i j 



intercellular mycelium. (After Millardet.) they attack living plants and 



often cause serious diseases 



of cultivated plants, entailing thousands of dollars of loss to the 

 horticulturist or farmer. Some of the important diseases caused 

 by them are downy mildew of the grape and cucumber, onion 



* This germination of eggs which have not been fertilized is sometimes 

 called parthenogenesis. 



