214 FIRST FORMS OF VEGETATION. 
especially the dog-lichen when growing in a damp 
and shady situation, and in the olive sea-weeds. 
The relative amount of these colouring matters 
varies with the degree of exposure to sun and 
air; and in this respect the Oscillatorias furnish 
a most interesting series of connecting links be- 
tween olive sea-weeds and lichens. When their 
vitality is very much reduced by want of light, 
their type of colouring closely approaches that of 
the olive sea-weeds ; whereas, when they are ex- 
posed to much air and light, the type approaches 
to that of such lichens as the Peltidea canina or 
Dog-Lichen. There is thus a striking analogy be- 
tween the results due to abnormally reduced or , 
increased vitality in the same kind of plants, and 
the normal characters of lower and higher classes 
of plants. 
Several obscure and curious organisms have 
been included by botanists in this vast and varied 
order of plants, some of which are supposed to be 
fungi in an embryonic or imperfectly developed 
state. They are composed of hyaline or coloured 
articulated filaments, aggregated together and 
forming a kind of fibrous crust, sprinkled over 
with loose granules. The localities where many 
of them are found prove that they are not genuine 
alge, or even independent organisms, but probably 
only the mycelia or spawn of various fungi. 
