i66 ANCIENT PLANTS 



coated genera, such as Corallina and others, have many- 

 fossil representatives. These plants appear so like corals 

 in many cases that they were long held to be of animal 

 nature. The genus Lithothamnion now grows attached 

 to rocks, and is thickly encrusted with calcareous matter. 

 A good many species of this genus have been described 

 among fossils, particularly from the Tertiary and Cre- 

 taceous rocks. As the plant grew in association with 

 animal corals, it is not always very easy to separate it 

 from them. 



Brown Alg^ (seaweeds) have often been described 

 as fossils. This is very natural, as so many fossils have 

 been found in marine deposits, and when among them 

 there is anything showing a dark, wavy impression, it 

 is usually described as a seaweed. And possibly it may 

 be one, but such an impression does not lead to much 

 advance in knowledge. From the early Palaeozoic rocks 

 of both Europe and America a large fossil plant is known 

 from the partially petrified structure of its stem. There 

 seem to be several species, or at least different varieties 

 of this, known under the generic name Nematophycus. 

 Specimens of this genus are found to have several ana- 

 tomical characters common to the big living seaweeds 

 of the Laininaria type, and it is very possible that the 

 fossils represent an early member of that group. In 

 none of these petrified specimens, however, is there any 

 indication of the microscopic structure of reproductive 

 organs, so that the exact nature of the fossils is not 

 determinable. It is probable that though perhaps allied 

 to the Laminarias they belong to an entirely extinct 

 group. 



An interesting and even amusing chapter might be 

 written on all the fossils which look like algae and even 

 have been described as such. The minute river systems 

 that form in the moist mud of a foreshore, if preserved 

 in the rocks (as they often are, with the ripples and rain- 

 drops of the past), look extraordinarily like seaweeds — as 



