DAMPING OFF. 245 



which when favorably situated will start the disease in fresh 

 plants. It is probably by the development of these in wet soil 

 during rain or at the time of watering the pots or soil in seed 

 beds that the disease is spread so rapidly. 



The fungus is however capable of developing as a saprophyte 

 on dead or partially decayed organic matter in the soil so that 

 with one watering it may become well seated in nearly all parts 

 of the bed. To show that it is also a saprophyte it is a very easy 

 matter to start it in the laboratory on the leaves or stems of seed- 

 lings which have been previously killed by boiling. 



This damping off fungus was first described by Hesse in 1874 

 (1. c.) and named by him Pythium debaryanum. It was shown 

 by him to be a parasite of seedlings, such as Camelina sativa, 

 Trifolium repens, Spergula arvensis, Panicum miliaceum and Zea 

 mays, while seedlings of Solanum tuber osum, Linum usitatissi- 

 mum, Papaver somniferum, Brassica napus, Ornithopus sativus, 

 Onobrychis, Pisum, Hvrdeum vulgare, Triticum vulgare and Avena 

 sativa were not attacked. 



DeBary made a comprehensive study of the sexual stage. 5 Py- 

 thium equiseti Sadebeck, is in his opinion the same species. P. 

 equiseti was first described by Sadebeck 6 in 1874 from prothallia 

 of Equisetum arvense, and in farther studies 7 it was shown that 

 not only did it occur in potatoes affected with Phytophthora infes- 

 tans* but that healthy potatoes could be inoculated with it. Py- 

 thium autumnale Sadebeck which grew in young plants of Equi- 

 setum palustre and E. limosum, produces oospores which develop 

 parthenogenetically. Fischer 9 places this in P. debaryanum, A 

 plant found in Lepidium sativum, and in Beta and Sinapis by 

 Lohde, 10 was described by him as Lucidium pythioides and from 



sBeitr. z. Morph. u. Phys. d. Pilze, IV. 1881. 



6 Ueber einen der familie der Saprolegniaceen angehorigen Pilze in dem 

 prothallien des Ackerschachtelhalmes. Sitzungsb. d. Bot. Ver. d. Prov. 

 Brandenberg, 116-122, 1874. 



7 Neue Untersuchungen iiber Pythium equiseti. Sitzsungsb. d. Gesells. 

 naturf. Freunde z. Berlin, V. 21, 1875. 



8 Ueber Infectionen welche Pythium-Arten bei labenden Pflanzen hervor- 

 bringen. Beibl. z. Tageb. d. 49 Vers. deutscher naturf. u. Aerlze. 100, 1876. 



9Rabenhorst's Krypt. Flora. Pilze, IV, 404, 1892. 



10 Ueber einige neue parasitische Pilze. Tagebl. d. 47 Vers. deutscher 

 Naturf. u. Aertze, 203, 1874. 



