ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1037 



presents several interesting peculiarities. Although reaching to over 

 50^ S. hit., it includes tropical types belonging to the genera Hypo- 

 pterytjium, Mniadelphus, and Hooheria. The flora which presents the 

 nearest rehitionshii) to that of Terra-del- Fuego is that of Kerguelen's 

 Land ; but here the tropical types are entirely wanting. 



Algae. 



Polymorphism of Algae.* — Dr. A. Hansgirg gives an historical 

 resume of the facts known with regard to the polymorphism of algae, 

 and then lays down the following propositions : — 



1. ]\lost, if not all, of the SchizophyccEe or Cyanophyceae are 

 polymorphic algaj, which occur in nature in different stages of their 

 development, whether unicellular or multicellular, and may, under 

 certain conditions, maintain themselves through many generations at 

 any particular stage ; their genetic connection can be proved by 

 observation of the history of their development. 



2. Most, if not all, of the algae hitherto included in the family 

 Chroococcaceae, belonging to the genera Ch-oococcus, Ghvoeapsa, 

 Aphaiwcapsa, Synechococcus, Glceotliece. Aphanothece, Chroodadylon, 

 Glaucocystis, Chtthrocystis, Polycystis, Coelosphserium, GompltospJiaeria, 

 Merismopedium, Chrootliece, and Bhodococcus, are connected genetically 

 with other more highly developed algae ; that is, they are descended, 

 by retrogressive metamorphosis, from various filamentous Schizo- 

 phyceae, which pass into the unicellular condition by their filaments 

 breaking up into separate cells. 



3. In the genera Leptotlmx, Hypheothrix, Spirulina, Oscillaria, 

 Phormidium, Chthonoblastns, Lynghya, Hydrocoleum, Symploca, and 

 ScMzothrix, belonging to the family Oscillariaceae, are numerous 

 forms most, if not all, of which are connected genetically, not only 

 with one another as younger and older stages, and with various 

 Nostochaceae and Chi'oococcaceac, by retrogressive metamorjjhosis, 

 but also with others belonging to the families Eivulariaceae, Scytone- 

 maceac, and Sii'osiphonaceae, as higher develojiments. 



4. The genera Nostor, Anabsena, Cylindrospermum, and Sphserozyga, 

 belonging to the family Nostochaceae, include many heterogenous 

 forms, wliich, like the Chroococcaceae, must be regarded as stages 

 of develoi)mcnt, analogous to certain zooglooa-conditions of the 

 Schizomycetes, of difierent species belonging to the groups Oscil- 

 lariaceae, Rivulariacea), and Scytonemaccae. 



5. In the genera Ca/othrix, Masticothrix, Mastigonema, ScJiizosiphon, 

 belonging to llivulariaceae, and in Diplocolon, Sci/toncma, Arlhrosiphon, 

 Tolyjjothrix, Plectonerna, and Gluucotlirix, belonging to tlie Scytone- 

 macea;, are included the highest developments of various alga3 

 hitherto mostly jilaced among Oscillariaceae. 



0. Just as the more liiglily developed Kivulariaceae and Scy- 

 t<jneinacea) may develope from various Oscillariaceae, so also from Glau- 

 cothrix, Tolypothrix, and Scytoiiema may arise the corresponding forms 



♦ Bot. Central bl., xxii. (1HS.5) pp. 24(5-51, 277-85, 308-10, 343-52, 373-83, 

 .38rj-4(t6; xxiii. (1885) pp. 229-33 (2 pl-s.). 



