ORDER III. 



LICHENES. Hoffm. 



Plants of less diversity of structure than the Musci or He' 

 paticcB ; consisting of a thallus, corresponding to the organs of 

 vegetation ; and of apothecia, corresponding to those of repro- 

 duction : unaffected by difference of temperature of the seasons 

 or of climates, hence more uniformly scattered over the earth's 

 surface than plants of the superior orders ; hence, too, they are 

 more rarely green on the surface, although the application of 

 moisture induces a slight greenish tint on nearly all ; of long 

 duration, and slow growth ; of peculiarly slow dissemination, 

 not appearing to be supplied with the means of expelling their 

 seeds at the period of maturity ; many, however, are furnished 

 with buds, an accessory mode of reproduction. Living on the 

 surface of soil, of rocks and of trees, they are neither properly 

 parasites on the latter, nor do they appear to draw any nutri- 

 ment from the former, their roots serving the simple purpose of 

 attachment. Lichens partially immersed in water, convey the 

 fluid to the parts that are not submerged. Beneath the super- 

 ficial or cortical layer of the thallus, is one green or becoming 

 green by abrasion. The Gongyli or seeds immersed in the 

 thallus cannot well be distinguished from those of the apothecia, 

 yet some observations point to the conjecture that the Gongyli 

 of the former produce thallus, and those of the latter apothecia. 

 The Lichens prefer the purest air and to face prevailing winds: 

 their Gongyli retain vivaciousness for long periods : new is- 

 lands emerged from the ocean at the distance of hundreds of 

 miles from land, soon exhibit the Lichens of the opposite wind- 

 ward shores, and form the first series of plants, the cradles of 

 future vegetation. 



