282 



GENERAL MORPHOLOGY OF PLANTS 



and yet the eggs ripen without fertilization 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. 



426. 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 annoyance by stop- 

 ping the flow of the waste 

 water. Flushing with 

 water often clears the 

 drain, but if the fungus 

 continues to be trouble- 

 some its growth can be 

 prevented by flushing the 

 drain now and then with 

 a weak solution of blue 

 vitriol. 



The Downy Mildews and 

 White Rust. 



427. The downy mil- 

 dews. The downy mil- 

 dews received this name 

 from the numerous sporo- 

 phores, 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 also a mildewed appearance. They are true parasites, 

 since they attack living plants and often cause serious diseases 

 of cultivated plants, entailing thousands of dollars of loss to 



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

 called parthenogenesis. 



Fig. 226. 



Downy mildew of grape (Plasmopora viticola) 

 showing tuft of conidiophores bearing conidia, also 

 intercellular mycelium. (After Millardet.) 



