132 THALLOPHYTA. [CH. 



cells figured by Williamson as possibly algae, endophytic in 

 the tissues of Coal-Measure plants, are no doubt thin- walled 

 vesicles which formed part of a highly vacuolated cell-contents. 

 Examples of such vesicles in living and fossil cells are shown 

 in fig. 42. The fact that the contents of living plant tissues 

 have been erroneously described as endophytic organisms, 

 should serve as a warning against describing fossil endophytes 

 without the test of good evidence to support them. 



The description of a fossil Nostoc by the late Prof Heer^ 

 from the Tertiary rocks of Switzerland cannot be accepted as 

 a trustworthy example of a fossil plant, much less of a genus 

 of recent algae. The application of recent generic names to 

 fossils which are possibly not even organic must do more harm 

 than good. 



II. SCHIZOMYCETES (Bacteria). 



It is impossible to draw a sharp line between the two sub- 

 divisions of the Schizophyta. The so-called Fission-Fungi or 

 Bacteria differ from the Schizophyceae or Fission- Algae in the 

 cell-contents being either colourless, blood-red or green, but 

 never blue-green. We may regard the Bacteria, generally, as 

 the lowest forms of plants ; they are extremely simple organisms 

 which have been derived from some primitive types which 

 possessed the power of independent existence and contained 

 chlorophyll — that important substance which enables a plant 

 to obtain its carbon first-hand from the carbon dioxide of the 

 atmosphere. 



Bacteria may be briefly described as single-celled plants, 

 and as de Bary suggested comparable in shape to a billiard ball, 

 a lead pencil or a corkscrew I A single spherical or cylindrical 

 cell measures about l/x in diameter^. They occur either singly 

 or in filaments, or as masses of various shapes consisting of 

 numberless bacterial cells. The nature and manner of life of 



1 Heer (55) vol. i. p. 21, PL iv. fig. 2. 



2 de Bary (87) p. 9. A good account of the Schizomycetes has lately been 

 written by Migula in Engler and Prantl's PJianzenfamilien, Leipzig, 1896. 



^ 1 fx = 0-001 millimetres. 



