108 TECHNICAL BULLETIN 4. 



were then sealed and kept in the laboratory. After two weeks, germina- 

 tion was found to be somewhat higher than in the case of spores from fresh 

 lesions. Tests at the end of four weeks gave 50 per cent germination. At 

 the end of three months the average percentage was not higher, though in 

 individual slides it mounted to about 65 per cent. A higher percentage 

 of germination has not been seen in any test. In removing these seedlings 

 from the damp earth it was constantly noticed that the soil remained cling- 

 ing to the lesions and could be washed off with difficulty, while it was very 

 easily removed from other parts of the plant. Microscopic examination 

 showed that the soil particles were attached by numerous fungous hyphse. 

 When these hyphse were transferred to sterile agar tubes they gave pure 

 cultures of Urocystis. It was not possible to determine whether these 

 hypha} arose from germination of spores in the sori, from vegetative hyphse 

 in the seedling or from both. If the spores germinate while still inside the 

 lesion, this may explain why not all the spores taken from the weathered 

 sori germinate; they may have already germinated. This experiment 

 demonstrates clearly one way, at least, in which the smut mycehum gets 

 back into the soil from the diseased planto. 



Natural Conditions of Germination. — It is a common impression among 

 laymen that the spore remains dormant in the ground, lying in wait until 

 an onion starts to grow near it, upon which it germinates and infects the - 

 onion. Such, however, is apparently not the case. The seedling does not 

 seem to furnish any stimulus which causes the spore to start. Whatever, 

 substances are necessary for starting the process are in the soil itself. As 

 soon as the spores are released into the soil — if not before — a few of 

 them germinate; the others become capable of germination gradually, 

 and it seems hkely that all of them finally come to germination, but that 

 the period of preparation differs in length for different spores, so that the 

 germination extends over many months and possibly years. This period 

 of preparation may be shortened artificially by the use of certain stimulat- 

 ing substances, such as cane sugar. 



The Process of Germination. 



Germination begins in three to six days ofter the spores are placed in the 

 water solutions or on agar plates as previously described. The time varies 

 somewhat with the medium used, and also apparently with other factors 

 which have not been explained. Three days are usually sufficient in 

 onion decoction or onion agar, while on soil decoction agar six da3's were 

 found necessary. 



The first indication of germination is the appearance of a hyaline hemi- 

 spherical vesicle (Fig. 1, B) on one side of the spore. This is apparently 

 an extrusion from the central fertile cell, but whether it comes out by a 

 rupture of the spore wall or by a regular pore could not be determined. 

 The covering of sterile cells renders exact observation of this point difficult. 

 This vesicle when first observed is of about the same size as one of the 

 sterile cells, and can at first be distinguished from the latter only by the 



