38 Myxophycese 



Stigonema in EPHKBE E. Fr., LICHENOSPHJSRIA Born., PTERYGIOPSIS Wainio and 

 SPILOMENA Born. 



Genera of the Rivulariacese in CALOTRICHOPSIS Wainio, HOMOPSELLA Nyl., LICHINA 

 Ag., LICHINELLA Nyl., LICHINODIUM Nyl., OMPHALARIA Gir. & Bum., POLYCHIDIUM Ach., 

 PTERYGIUM Nyl. and STEINERA Zahlbr. 



The actual species are known only in a few cases : Glceocapsa montana in B^EOMYCES 

 ROSEUS and OMPHALARIA UMBELLA ; Nostoc sph&ricum in the Collemaceous HYDROTHYREA ; 

 Nostoc punctiforme in PELTIGERA, PANNARIA and STICTINA ; Rivularia nitida in POLY- 

 CHIDIUM, OMPHALARIA, LICHINA, etc. ; Stigonema panniforme in EPHEBE PUBESCENS. 



With regard to the geographical distribution of the Myxophycese we have 

 at present a wide knowledge but an insufficiency of detail. There are 

 undoubtedly a large number of cosmopolitan species which occur all over 

 the world and in all climates, a fact which is probably due in part to the 

 primitive and ancient character of the organisms, and very largely to their 

 capacity for withstanding drought and extremes of heat and cold. 



Camptothrix, Chondrocystis, Katagnymene, Loefgrenia, Polychlamydum, 

 Proterendothrix, Porphyrosiphon and Trichodesmium are, so far as is known, 

 typically tropical and subtropical genera. A vast amount of detailed and 

 accurate taxonomic work is necessary, however, before any reliable state- 

 ments can be made concerning the geographical distribution of the Blue- 

 green Algae. 



AFFINITIES. It has been customary to regard the Myxophycese as 

 organisms of a primitive type closedy allied to the Bacteria. This view 

 received much encouragement by the general acceptance of Cohn's 

 ' Schizophy ta ' as a group put forward to embrace the Schizomycetes 

 (Fission Fungi or Bacteria) and the Schizophyceae (Fission Algae). Modern 

 evidence, however, does not wholly support this view, and there is little 

 doubt that the Bacteria and Myxophyceae are separated by a gulf much 

 wider than would be thus indicated. Cohn's name ' Schizophyceae ' should 

 be entirely discarded as- it is very misleading. Far from being the ' Fission 

 Algae,' only a small percentage of the known species divide by that gradual 

 constriction which is so characteristic of the vast majority of Bacteria. Cell- 

 division in the filamentous forms is generally by the gradual formation of 

 a transverse septum. 



At present it is necessary to make very guarded statements concerning the comparative 

 cytology of the two groups. The investigation of that giant Bacterium Hillhoiisia has 

 shown that the dry-staining methods so much in vogue in studying the cytology of both 

 the Bacteria and the Myxophycese are to a considerable extent unreliable, and it is also 

 possible that the bacterial protoplast may show various grades of simple structure. It is 

 quite possible that true chromatin such as occurs in higher organisms does not exist in 

 the bacterial cell, and the chromatin-substance which does occur is only present in the 

 form of very minute granules. The chromatin-substance present in the protoplast of 

 Ilillhousia cannot be recognized by staining, and in the Blue-green Algee it is exceedingly 



