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^), it is possible to show, by 

 leaving one out at a time, that each of the salts mentioned 

 is 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. 



K by rubidium or csesium, 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 (Berberis vulgaris). 



The same thing is true of other Uredinece. 



(83) Hanging-drop cultures. 



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



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

 chemicals themselves. 



2 See Nageli, Erncihrung der niederen Pilze. 



3 H. Marshall Ward, Philosophical Transactions, 1892, b, p. 130. 



