70 FUNGI. [CH. Ill 



C. Hardly perceptible growth which soon stops. 



D. Fair growth at first, ceasing soon. 



E. Standard growth, rapid and large. 



If sufficient care is taken as to absolute purity (a 

 difficult bit of manipulation 1 ), it is possible to show, by 

 leaving one out at a time, that S, P, K, Mg are necessary ; 

 Ca is not necessary. 



Also to show that, with Penicillium, magnesium sul- 

 phate can be replaced by magnesium sulphite or hyposul- 

 phite, but not by some other sulphur compounds. 



The question whether K can be replaced by Rb or Cs 

 is not decided : it seems clear that it cannot be replaced 

 by Na or Li. See Pfeffer, Pflanzenphysiologie, Ed. n., 

 vol. I., p. 404. 



(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 (Berberis vulgaris). 



The same thing is true of other Uredinece. 



(83) Hanging-drop cultures. 



A damp-culture cell is to be prepared as follows 3 . A 



1 Owing to the cotton-wool, dust, glass, water &c. rather than the 

 chemicals themselves. 



2 See Nageli, Ernahrung der niederen Pihe. 



9 H. Marshall Ward, Philosophical Transactions, 1892, B, p. 130. 



