260 DISEASES OF FIELD & GARDEN CROPS. [OH. 



tubes, and the two fused tubes will giv^ rise to a third 

 common conidium-bearing tube. Sometimes this tube is 

 extremely long and fine, and furnished with numerous 

 joints throughout its entire length. The conidia, as pro- 

 duced by the germ-tubes, are capable of producing other 

 conidia by budding, till at last large colonies of conidia 

 are produced in a yeast- like condition, free from the 

 original Ustilago spore and its septate germ tube. The 

 conidia, which are very unequal in size, germinate as at 7 

 and 8. Germination may take place at one or both ends 

 or one or both sides, and the germ-tubes may fuse with 

 each other at any point of contact. Sometimes the germ- 

 tubes produced by the conidia are of almost inconceivable 

 fineness and attenuation, but always more or less jointed 

 throughout their entire length ; the contained vital ma- 

 terial is generally most abundant at the growing end. 

 Sometimes, when growth has quite ceased, owing to 

 unfavourable conditions, it is renewed with vigour under 

 changed conditions, and new colonies of yeast-like conidia 

 are formed, either from old threads or old conidia. 



In the allied fungus named Ustilago antherai'um, Fr., 

 the conjugation of cells is very clearly seen, and lateral 

 conidia are produced, as in Tilletia, Fig. 116, D, G. This 

 parasite is common on the flowers of Silene, Lychnis, etc., 

 in fields and hedge sides, reducing the anthers with their 

 pollen to black dust. The conjugation is also very dis- 

 tinct in the spores of Ustilago longissima, Tul. ; common 

 on Poa aquatica, L., and P. fluitans, Scop. No doubt the 

 so-called conjugation of cells is potential in all species of 

 Ustilago and its allied genera. 



We recently observed the germination of the spores of 

 Ustilago carbo, Tul., under curious and natural conditions. 

 "We placed a large number of spores on the top of a 

 flower-pot filled with moist white sand to note whether 

 the spores would be readily filtered through the mass by 

 rain. They did so filter in large numbers ; but many of 

 the spores germinated on the top stratum of sand, and 



