138 THALLOPHYTA. [CH. 



Renault has pointed out that fossil Bacteria may often be 

 more readily detected than living forms owing to the presence 

 of a brown ulmic substance which results from the carbonisation 

 of the protoplasm. He is forced to admit, however, that such 

 diagnostic characters as are obtained by Bacteriologists by means 

 of cultures cannot be utilised when we are dealing with fossil 

 examples ! We are told that " Partout on nous avons cherch^ 

 des Bacteriace^s, nous en avons rencontre."^ This indeed is 

 the danger; an extended examination of fossil sections under 

 an immersion-lens must almost inevitably lead to the discovery 

 of minute bodies of a more or less spherical form which might 

 be Micrococci. To measure, and name such bodies as definite 

 species of Micrococci is, I believe, but wasted energy and an 

 attempt to compass the impossible. 



Specialists tell us that the accurate determination of species 

 of recent Bacteria is practically hopeless: may we not reasonably 

 conclude that the attempt to specifically diagnose fossil forms 

 is absolutely hopeless ? " The imagination of man is naturally 

 sublime, delighted with whatever is remote and extraordi- 

 nary — " , but it is to be deplored if the fascination of fossil 

 bacteriology is allowed to warp sound scientific sense. 



IV. ALGAE. 



A. DIATOMACEAE. (Diatoms.) 



B. CHLOROPHYCEAE. (Green algae.) 



C. RHODOPHYCEAE. (Red algae.) 



D. PHAEOPHYCEAE. (Brown algae.) 



The presence of chlorophyll is one common characteristic 

 of the numerous plants included in the Algae. The generally 

 adopted classification rests in part on an artificial distinction, 

 namely the prevailing colour of the plant. 



It must be definitely admitted, at the outset, that palaeo- 

 botany has so far afforded extremely little trustworthy infor- 

 mation as to the past history of algae. Were we to measure 



1 Renault (963) p^ 277. 



