112 TECHNICAL BULLETIN 4. 



III. Sapeophytism. 



The early botanists and mycologists believed that smut fungi were obli- 

 gate parasites, i.e., they developed only when in parasitic relation with host 

 plants from the living cells of which they must take their nourishment. 

 We now know, however, that at least most smut fungi have in their life 

 cycle a saprophytic period during which they may develop extensively 

 and propagate for a long time, deriving nourishment only from dead 

 organic material in the soil or other substrata. Also most of them may 

 be propagated indefinitely in artificial culture media of various composi- 

 tions. Our knowledge of this stage began ^vith the extensive investigations 

 of Brefeld (3), and has been increased later bj'' numerous smaller contribu- 

 tions from a large number of workers. Urocystis ceptdae is no exception to 

 the rule, and is very readily isolated and grown in a large number of cul- 

 ture media and on soil. It is probably able to exist and grow in the soil for 

 years in entire absence of onions. 



Isolation. 

 Two methods of isolation have been used by the writer. By the first 

 method a germinating spore on an agar plate is located under the micro- 

 scope by a ring of India ink, care being taken that this spore is far enough 

 removed from all others to prevent confusion. WTien themycelium from the 

 germinating spore has increased to such an extent that it is visible to the 

 naked eye as a tiny white speck it is transferred to an agar slant where it 

 gradually spreads to the agar of the tube and can be grown for a long 

 period. This method was used especially in the original isolations when 

 it was necessary to know for certain that the resulting fungus originated 

 from a single spore of Urocystis cepulae. In later work a more rapid method 

 was used. A part of a cotyledon or young leaf containing a lesion which 

 had not yet broken open was washed for a few minutes in mercuric chloride 

 1 to 1,000 and then in sterile water. The lesion was then cut into as many 

 pieces as desirable and the pieces transferred to agar slants. One hundred 

 per cent of pure cultures could be obtained in this way. Lesions of any 

 age could be used, but the youngest were found to be most satisfactory. 



Cultural Characters. 

 The range of media on which the fungus will develop is almost unlimited. 

 Those which the WTiter has used are listed below along with a brief state- 

 ment of the pecuharities exhibited by the organism on that particular 

 medium. 



Potato Agar. 



The ordinary potato agar containing a boiled decoction from a large potato and 

 17 grams of agar to a liter of water. No sugar was added and the acidity was not 

 determined. Growth very slow, reaching a diameter of 1 cm. in about ten days; 

 very dense and compact like fine felt, snow white, dry, fiat, but with considerable 



