6 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



LIFE HISTORY OF THE SMUTS. 



In the study of these fungi, there are three parts that we 

 need to consider, namely, the mycelium, the spores, and the 

 sori. 



Mycelium is the technical name for the vegetative part of 

 the smut, by means of which it spreads through its host and 

 gathers nourishment. This consists of microscopic threads 

 confined to the interior of the host, so it is necessary to exam- 

 ine very thin cross sections of the tissues under the micro- 

 scope to see this stage. See Fig. 26. These threads vary but 

 little with the different species, and therefore are of no value 

 in classifying the different species. They are simple, hyaline, 

 more or less branched, and at first filled with protoplasmic 

 contents, but gradually lose most of their contents and be- 

 come septate. They push their way between the cells of 

 the host or sometimes through them. Usually, however, they 

 enter the cells only by short special branches called haustoria, 

 whose special function is to gather nourishment from the cell. 

 The mycelium may be localized or rather generally spread 

 through the host. In those cases where it gains entrance 

 through the germinating seed, it usually remains evident fi- 

 nally only at the nodes or where it breaks forth to the exterior 

 in its fruiting stage. In perennial plants the mycelium often 

 becomes established in the perennial parts, from which each 

 year it sends threads into the new growth. 



Eventually the mycelium becomes prominent in certain 

 regions of the host, and there undergoes special modification 

 to give rise to the reproductive or spore stage. The walls of 

 the mycelial threads that form the spores are generally indis- 

 tinct through more or less complete gelatinization. The 

 spores are usually formed from contents in the interior of 

 these fertile threads. This gelatinization apparently serves 

 to nourish the developing spores, as often all signs of the 

 threads disappear on maturity of the spores. In some cases, 

 as in the genus Neovossia, Fig. 13, and often in Entyloma, 

 however, these threads remain as more or less evident envel- 

 opes to the spores. 



Spores are the bodies by which the smuts reproduce them- 

 selves. See Figs. 1-20. They are the evident, usually ex- 



