74 



POPULAR HISTORY OP LICHENS. 



irregularly or in groups, over different parts of the surface 

 of the thallus. He will then ascertain that the spermatia 

 precede the spores, sometimes by several months ; that, while 

 he finds the former in autumn or winter, he may not discover 

 the latter till the following spring or summer ; and that by 

 the time the apothecium and spores are mature, the spermo- 

 gone is an empty or shrivelled cyst, all trace of the sper- 

 matia having disappeared. Ignorance of this circumstance 

 is one great cause why their existence has been so long 

 overlooked; for observations on the reproductive system of 

 Lichens have chiefly been made on plants whose apothecia 

 had arrived at maturity. Keflection upon the analogies of 

 the subject however will make it apparent that we can as 

 reasonably expect to find mature spermatia in their spermo- 

 gones, co-existent with mature spores in their apothecia, as 

 to discover stamens in phanerogamic plants when their seeds 

 are ripe. Another great cause of the total absence hitherto 

 of a knowledge of the characters or functions of the spermatia 

 is undoubtedly their extreme tenuity, and the consequent 

 necessity of applying high powers of the microscope to their 

 examination. In our speculations on the influence of the 

 spermatia upon the spores, it is important to bear in mind 

 that, in regard to their position on the plant, the spermo- 



