54 PLANT DISEASES 



fungus emits a long tube which passes through the tissue 

 of the host, and through this tube the zoospores formed in 

 the fungus cell escape, and inoculate other plants. Thick- 

 walled, warted resting-spores are also present in the epi- 

 dermal cells of the host. 



Preventive Means. — Dry, airy localities should be 

 selected for seed-beds. Where the disease has existed, 

 the ground should not be used for the same purpose for 

 some time. Remove and burn dying plants to prevent 

 the resting-spores remaining in the soil. 



Woronin, Rungsh. Jahrb. 1878, p. 557, pi. 31, figs. 12-16. 



'DAMPING OFF' 



{Pythium de baryanum, Hesse.) 



The term 'damping off' is applied to-a disease of seed- 

 lings, characterised by the falling over and dying of the 

 plan tlets, due to the destruction of the fundamental tissue 

 of the stem just above ground by a fungus called Pythium 

 de baryanum. Seedlings of cruciferous plants are more 

 especially attacked, but it also attacks maize, millet, clover, 

 mangel, cucumber, and has been recorded as occurring on 

 the prothalli of Lytopodium and Equisetum. Conidia, 

 sporangia, and sexually produced oospores are formed by 

 the fungus, but never in the tissues of the host, always on 

 its surface, or on the adjoining soil, if sufficiently wet. 



The conidia form one or two germ tubes almost immedi- 

 ately after they are mature ; or, under certain circumstances, 

 after a longer or shorter period of time, even extending to 

 several months. A second kind of conidia require a period 



