PYTHIUM 491 



IV. PERONOSPORE.E 



PYTHIUM DE BARYANUM 



I. Sow seeds of the common garden Cress (Lepidium 

 sativum) thickly in a flower-pot : cover it over with a 

 glass plate, and keep it well watered, so that the young 

 seedlings grow up in an atmosphere saturated with water. 

 After a few days the heads of some of the seedlings may 

 be seen to have bent over, owing to insufficient support 

 of the stem : examination will show that the curvature 

 is a sharp one, so that it is not due to general 

 weakness : further that the stem is thin and flabby 

 at the point of curvature : while fungal filaments 

 may be observed in close contact with the stem at 

 that point, and it is this Fungus (Pytliium de Baryanum) 

 which is the cause of the disease termed by gardeners 

 " damping off " : it is of common occurrence in pro- 

 pagating pits which are kept too warm and moist. 



Other members of this, and other allied genera may also be 

 present, but the species above named is almost certain to appear 

 on damp cultures of the common Cress : the difficulty of dis- 

 tinguishing these species from one another may cause apparent 

 discrepancy between the observations and the description given 

 below. 



