NUTRITIVE ORGANS OF CELLULAR PLANTS. 319 



become developed in amanner very different from what it 

 was at first, and this explains the existence of those speci- 

 mens, so different in various parts of the Thallus, which 

 have been produced at different periods of vegetation. 

 These examples tend to prove that some Lichens, which 

 might be thought to be of a different species, or even 

 genus, are, in reality, only different states of the same 

 species. 



These interruptions of the life of Lichens, is con- 

 nected with their longevity, which appears much greater 

 than would be expected in plants so insignificant ; thus, 

 Vaucher observed after forty-five years the same indi- 

 dual of Loharia pulmonaria attached to the same place 

 on the same tree. 



The colour of individual plants frequently varies, 

 according to the degree of atmospheric moisture ; it 

 usually becomes green when the tissue is very wet, and 

 coloured white, green, black, yellow, or orange-red, 

 when it is dry. 1 have remarked, that all those Lichens 

 which are green, or are capable of becoming so under 

 water, disengage oxygen gas when exposed to the solar 

 rays ; whilst this phenomenon does not take place in the 

 species which are not green, nor capable of becoming so 

 under water. 



Section V. 



Of Fungi. 



Fungi, considered in that point of view in which we 

 are here occupied, only present cellules, sometimes 

 round, at others elongated under the form of hollow 

 filaments, which seem to be fibres ; sometimes very close 



