DISPERSION. 317 



insects have been at work, destroyed the threads, 

 and left behind them characteristic cyHndrical 

 exuviae. These undoubtedly had passed through 

 their bodies, for fragments of threads were mixed 

 with the spores. On two or three occasions we have 

 determined that such spores still possessed the 

 power of germination, even perhaps in an increased 

 degree. These insects may assist in the dissemina- 

 tion of such spores, as molluscs do in feasting on the 

 gills of an agaric, and then retiring to the shelter of 

 some prostrate trunk. These speculations, however, 

 concern a very minute class of organisms which, as a 

 rule, we have deemed it prudent to ignore in this 

 volume. 



Then there are larger animals which contribute 

 their share to the dissemination of plants, and espe- 

 cially those of the human family. It would be im- 

 possible to enter fully on such a topic, at the end of 

 a chapter, but one or two brief suggestions may 

 be permitted. Even to the present day, writes 

 Schleiden,^ are marked the footsteps of the bands 

 of nations which in the middle ages emerged from 

 Asia into Central Europe, by the advance of the 

 Asiatic steppe plants, such as the kochia and the 

 Tartar sea-kale, the former into Bohemia and Car- 

 mola, the latter into Hungary and Moravia. The 



> Schleiden, "The Plant," p. 301. 



