1890.] PUBLIC DOCUMENT — No. 33. 203 



structure than true seeds, and are usually microscopic in 

 size. 



In the simplest cases, the spores of a fungus are produced 

 directly on the ends of separate and independent fruiting 

 threads ; in other cases they are the products of sexual proc- 

 esses, involving the union of distinct male and female threads ; 

 and, in the more complicated forms, numerous reproductive 

 threads become intimately interlaced and compacted into a 

 fruiting structure, often of considerable size, which bears 

 spores in an interior cavity or cavities, or on some part of its 

 surface. These spore-bearing structures reach their greatest 

 development and conspicuousness in the " toadstools " and 

 related fungi. In the modes in which spores are developed 

 from the fruiting threads, we may distinguish two chief types. 

 In one case, the end of a thread is simply cut off to form 

 a spore ; while, in the other, the end of the thread swells, 

 and spores are formed free in the swollen portion. Those 

 of the former type may be called naked, those of the latter, 

 enclosed, spores. There is another classification of the 

 spores of fungi, which is of special importance in the study 

 of plant diseases. The majority of fungus spores can ger- 

 minate at once and produce new fungi, under favorable 

 conditions for vegetation. Of these there are some which 

 live but a short time, and, unless they very soon find such 

 conditions, fail to develop. They are produced in great 

 numbers, however, may develop rapidly, and serve especially 

 to spread the fungus by the infection of new hosts during 

 the growing season. They may therefore be designated 

 suiviMER SPORES. A familiar example is offered by the 

 spores developed in red-brown streaks on the leaves and 

 stalks of grain, in midsummer, and known as the "red rust." 

 Other spores can live for a long time, awaiting suitable con- 

 ditions, and ready to improve the first opportunity for 

 germination. Still others, on the contrary, require a greater 

 or less period of rest or quiescence before germination can 

 take place. Such spores are usually able to withstand great 

 extremes of temperature and dryness, and serve to perpetu- 

 ate the plant through the winter or other unfavorable period ; 

 in contrast to the summer spores, which spread it rapidly at 

 favorable seasons. They may l)e distinguished as resting 



