102 TECHNICAL BULLETIN 4. 



Immersed in the liquid they do not germinate as readily as when floating on the 

 surface. Thus, after eighteen hours on one occasion, the spores in the water had 

 failed to germinate, while by simply altering the focus and examining the spores 

 on the surface they were all found, with very few exceptions, to have germinated. 



In the descriptions of germination given by the majority of writers 

 there is no way of determining just how much influence the presence of 

 air had. 



It seems probable that, in general, the presence of air is essential to 

 the germination of smut spores, but that different species vary in respect 

 to the amount required; some need scarcely any, others must have verj^ 

 free access to air, and there are probably all gradations between these two 

 extremes. 



Nutrient Solutions. — Very early in the investigation of smut spore 

 gennination it became apparent that the spores of some species could not 

 be germinated merely by placing them in water when mature. Conse- 

 quently solutions of various substances supposed to have nutritive quali- 

 ties have been tested for their ability to induce germination. Hallier (6), 

 in 1868, was apparently the first to use such solutions. He used a great 

 many substances such as albumin, starch, milk, sugar solution, etc. Others, 

 since then, have used almost every kind of a salt, acid, or other substance 

 for which one could imagine any germinative influence. One should con- 

 sult Osner's (13) bulletin on "Leaf Smut of Timothy" to gain some idea of 

 the number of substances that can be used for that purpose. IMcAIpine (11) 

 seems to have had most success with a hay infusion, although he also used 

 various other solutions. Sugar solutions and decoctions of the host plant 

 have proved fairly successful. 



The nutritive solution which has been used most extensively and proba- 

 bly most successfully is the "nahrlosung, " a sterilized aqueous decoction 

 of horse dung which was employed first by Brefeld (3, 4). In this "nahr- 

 losung" he was able to bring to germination the spores of many species 

 which showed no sign of germination in water, e.g., Cintractia spinificis 

 (Ludw.) McAlp. (McAlpine (11) also confirmed Brefeld's results), Doas- 

 sansia Limosellae Kunze, Ustilago Andropogonis tubercidati Bref., Ust. 

 Arundinellae Bref., Ust. Coicis Bref., Ust. Cynadontis Hem., Ust. Ischdemi 

 Fckl., Ust. major Schroet., Ust. Panici leucophaei Bref., and Ust. T^dasnei 

 Klihn. Other species, e.g., Ust. Maydis, which gave scanty or only occa- 

 sional germination in water, germinated to almost 100 per cent in this 

 "nahrlosung." In almost every case the growth and size of the germ tube 

 (promycelium) was increased; and frequently sporidia were produced in 

 this nutritive solution where none at all were developed in water. On the 

 whole, however, it should be kept in mind that in by far the majority of 

 cases the function of the nutritive solution was to bring the germling to 

 complete development after it had started, rather than to cause it to start 

 in the first place. Only in the case of the comparatively few species men- 

 tioned above did he fail to get some germination in water also, and very 

 commonly the percentage of germination was as high in water as in "nahr- 



