CH. Ill] FUNGI. 63 



phate can be replaced by magnesium sulphite or hyposul- 

 phite, but not by some other sulphur compounds. 



K by rubidium or caesium, but not by Na, Li, Ba, Sr, 

 Ca, Mg. 



Ca by Mg, Ba, or Sr, but not by K or Na\ 



(82) Puccinia. 



Obtain teleutospores of Puccinia graminis which have 

 wintered on the straw of wheat or Triticum repens, and 

 sow in February — April in, (A) water, (B) nutritive solu- 

 tion, and keep at 10 — 15° C. in the dark. 



Both will germinate, and even proceed to develope the 

 "sporidia," but these die off eventually. 



Their further developement can only be got by infecting 

 young leaves of the Barberry. 



The same thing is true of other ITredinece. 



(83) Hanging-drop cultures. 



A damp-culture cell is to be prepared as follows I A 

 deep glass ring is placed on a broad glass slide and a 

 drop of previously sterilised olive oil allowed to run in, or 

 melted paraffin may be run in, in the same way while the 

 slide and ring are hot ; this cements the ring to the slide, 

 while a cover-slip placed on the ring like a roof supports 

 the hanging drop. Or a chamber may be made as 

 described and figured by Marshall Ward, loc. cit. p. 131, 

 which is especially useful where it is desired to control the 

 nature of the atmosphere to which the drop is exposed. 



^ See Nageli, Emahrung der Niederen Pilze. 



' H. Marshall Ward, Philosophical Transactions, 1892, a, p. 130. 



