58 



POPULAR HISTORY OF LICHENS. 



is now generally acknowledged to be the fertilization or fe- 

 cundation of the spores : and 3. Pycnides, which give rise 

 within their cavities to spore-like bodies, termed Stylospores, 

 whose precise office in the physiology of reproduction does 

 not appear yet to have been accurately determined. The 

 Secondary reproductive system consists of the Gonidia, of 

 which we have already spoken. While the spore is a cel- 

 lular embryo, a reproductive cell prepared by a process of 

 fecundation, destined to the propagation of the species, 

 the gonidium is a cellular bud, a reproductive cell, which 

 has undergone no preparatory fertilization, destined to mul- 

 tiply the individual. As we have seen, the latter may multiply 

 either on some part of the parent thallus, — as in the folioles 

 or squamules of the podetia in the Cladonia, — or external 

 to the parent thallus, as in the rudimentary vegetative system 

 of the same genus. The apothecia are generally easily re- 

 cognizable on some part of the thallus ; they have long been 

 familiar to Lichenologists, some of whom have taken their 

 characters as the basis of classification. The Spermogones 

 and Pycnides have only been fully discovered and described 

 within the last few years : a knowledge of their structure and 

 relations is the key to many hitherto difficult problems in 

 the natural history of the Lichens. The former are so minute 



