88 BOARD OF AGRICULTURE. [Pub. Doc. 



and swell up, thus forcing the spores out through the open- 

 ing in the top. Carried by the wind or other agencies to the 

 young foliage of the budding trees, they germinate, force 

 their way into the succulent tissues, and finally produce the 

 first crop of summer spores upon the leaves or twigs. 

 Familiar examples of such winter spores are seen in the 

 strawberry blight, the powdery mildews, and the black-rot 

 of grapes. 



Again, some fungi produce, late in the season and gener- 

 ally within and therefore protected by the tissues of the 

 plant, peculiar roundish bodies, called resting -sjjores, from 

 the fact that, unlike the summer spores, they require a 

 period of rest, after they have reached maturity, before they 

 will germinate. These resting spores may be formed either 

 from a small portion of one of the vegetative threads, which 

 swells slightly and takes on a hard, thick wall, or, as in the 

 case of the downy mildews, from a special form of fruiting 

 branch, the tip of which swells up into a globular vesicle, 

 containing a single large spore w^ith a very dense wall, buried 

 in the tissues of the host-plant. As contrasted with the 

 minute and short-lived summer spores, the winter and rest- 

 ing spores are large and few in number, but their thick walls 

 and protective surroundings enable them to resist extremes 

 of cold and drought fatal to the other forms, and they thus 

 serve in many cases to carry the fungi over the winter. 

 With the approach of warm weather they start into growth 

 again, and either directly or indirectly give rise to a crop of 

 summer spores. 



Some fungi, however, possess neither of these forms of 

 resistant spores, and other methods are resorted to, to main- 

 tain vitality. The vegetative threads of some fungi when 

 placed under conditions unfavorable to growth, become 

 twisted into dense knots of a solid consistency and with a 

 hard, black exterior. These knots are known as sderod'a, 

 and are sometimes as large as a kernel of corn. Familiar 

 examples of sclerotia are seen in the ' ' ergot " of rye and 

 in the rot of lettuce grown under glass. They are extremely 

 resistant, and maintain their vitality sometimes for years. 



In the case of other fungi the vegetative threads are per- 

 ennial in the tissues of the plant affected, and in such cases 



