ROOT CROPS. 



43 



reduce its vitality considerably. When artificial cultures 

 were exposed to a temperature of — 17° C. for one day, the 

 organisms were completely destroyed. An E.M.F.i of 

 3'3 volts (at 17° C.) destroyed B. allii when growing in 

 sterilized pork broth (neutral). 



Prevention. — Onions, lohen stored, should be kept in a 



Fig. 17. — Onion Mildew (Peronospora ScUeideniana). 



A. The fuBgDS growing from the base of an onion leaf. 



B. Mycelium ramifying amongst the cells of the host-plant. 

 0. Stomata of leaf. 



D. Conidia (spores). 



{ X 50 diameters. ) 



perfectly dry place, or they may become a prey to this 

 microbe.^ 



The Onion Mildew {Peronospora Schleideniana, 

 Fig. 17). This fungus is closely allied to Peronospora 

 infestans (the potato-disease fungus), and, like all the 

 members of the Peronosporeee, grows within the leaves 

 and stems of the host-plant. The onion mildew causes 



1 An electro-motive force (see any small text-book on electricity). 



2 For further information see Dr. Griffiths' papers in the Proceed- 

 ings of the Royal Society of Edinburgh, vols. xv. and xvi. ; and 

 Comptes Btndus, vol. ex. 



