100 TECHNICAL BULLETIN 4. 



II. Germination- of the Spores. 



The spore of Urocystis cepulae is compound, ha\'ing one large central 

 fertile cell to the surface of which are attached 15 to 40 smaller hemi- 

 spherical sterile cells. There are said sometimes to be two fertile cells at 

 the center, but in a thiee-year study of the fungus the MTiter does not 

 remember ever having seen a spore ^\ith more than one. To conform to 

 the nomenclature of certain other genera of smuts, the entire structure is 

 usually called a spore ball, the peripheral cells being termed pseudospores. 

 Since we have here only one cell capable of germination,^ it is perhaps 

 better to term the whole structure a spore and then distinguish between 

 fertile and sterile cells. The hemispherical cells are attached to the fertile 

 cell by their flat surfaces, but do not cover it entirely. The}' stand apart 

 as indicated in Fig. 1 (page 109). The sterile cells are tinted bro\\Ti, while 

 the central cell is a more solid opaque browoi. Sterile cells average 5/z in 

 diameter by 4.25/z in height. The fertile cell is usually spherical, but 

 frequently oval or ovate, averaging about 12« in diameter. The entire 

 spore averages about 19// in diameter. 



For the germination of most fungous spores it is only necessary to place 

 them when mature in a drop of water, and, after a few hours, or, at most, 

 a few days, the whole process may be watched under the microscope. 

 But for Urocystis cepulae the case is not so simple. Germination tests, 

 conducted in the same way in which the writer had brought to germina- 

 tion the spores of many species of fungi, were entirely without result for 

 the onion smut fungus. Apparently' there are other essential conditions 

 which had not been obtained in these trials. This preliminary failure led 

 to a thorough search through the literature to find what conditions were 

 essential for the germination of spores of other species of Ustilaginales. 

 It seemed probable that the same conditions which brought about germi- 

 nation in other smuts might also be successfulh' applied to Urocystis cepulae. 

 A condensed summarj' of the literature of this phase is given below, fol- 

 lowed by a description of the experiments v^ith the spores of Urocystis 

 cepulae. 



Review of the Literature on Essential Conditions for Smnt Spore Germination. 

 The Water Requirement. — No spores will germinate without water in 

 some form, sometimes, to be sure, merely as vapor in a saturated air. In 

 the simplest cases, and, in fact, for the majoritj'^ of the smut fungi, it is 

 only necessary to immerse the spores, as soon as mature, in a drop of water 

 on a slide, or in a hanging drop. Enough air to satisfy all requirements 

 seems to be present dissolved in the water, or else the spores remain on the 

 surface of the drop. Brefeld (3), in his experiments, germinated the spores 

 in a film of water which adhered to the inside of the walls of flat glass 

 chambers after the bulk of the li(iuid had drained out. This probably in- 

 sured greater access to air than where the hanging drop or drop on slide has 

 been used, and this fact should be kei)t m mind in interpreting his results. 



