INTRODUCTION. XV11 



forms which like the many Chroococcaceae forms, are arrested 

 conditions of development resulting in many instances from 

 sudden thermic and hygrometric changes, and should be treated 

 as developing conditions of various species of the families 

 Oscillariaceae Bab., Eivulariaceae Eab., and Scytonemaceae Eab. 



THESIS V. The forms of the genera Mastigothrix Kg. , Mastigo- 

 nerna Swabe, Schizosiphon Kg., belonging to the Family Eivulari- 

 aceae Eab. , and of the more recently added genus Calothrix, and 

 also the forms of the genera Diplocolon Naeg., Scytonema Ag., 

 Arthrosiphon Kg., Tolypothrix Kg., Fleet onema Thur., Glau- 

 cothrix Kirch., and others of the Family Scytonemaceae Eab., 

 are the higher, and the most highly developed Algae forms. 



THESIS VI. As the higher developed forms of Eivulariacea3 

 Eab. , (Calothrix Thr. ) and of Scy tonemaceae Eab. , may be devel- 

 oped from forms of the Family Oscillariaceae, so are, or may be, 

 developed from the genus Glaucothrix Kirch., forms of Toly- 

 pothrix Kg., Scytonema Ag., or forms of the nearly related 

 Family Sirosiphoniaceae Eab., as the genera Hapalosiphon Naeg., 

 Sirosiphon Kg., Stigonema Ag., Fischera, Schwabe, and others. 



THESIS VII. As the most of the Schizophyceae, so also many 

 of the Chlorophyceae are polymorphic algae. Most of the Chlo- 

 rophyl-green filamentous algae as Microspora Thr., Conferva 

 Link., Ehizoclonium Kg., Ulothrix Kg., Schizomeres Leib., 

 and Schizogoniuni Kg. , stand in close relation to the higher forms 

 as of the Family Clisetophoraceae Eab., Siphonocladiaceae Schmitz, 

 Ulvaceae Eab., and others, which forms are produced by the 

 widening of the single filaments and the dividing longitudinally, 

 thus gradually producing leaf-like forms ; on the other hand, by 

 the separation of the parts and division of the cells in one, two 

 or three directions, the most of the so-called unicellular algae are 

 produced, embracing forms of Protococcus Ag., Palmella Lyngb., 

 Pleurococcus Menegh., Gloeocystis Naeg., Palmagloea Kg., 

 Schizochlamys A. Br., Palmodactylon Naeg., Dictyosphaerium 

 Naeg., Apiocystis Naeg., Polyedrium Naeg., Characium A. Br., 

 Hydrianum Eab., and others. * 



Dr. Hansgirg does not in every instance demonstrate the posi- 

 tion taken, but he does take up several species and follows them 

 minutely through various polymorphic changes which occur in 

 the process of multiplication ; he also describes phases which 

 occur under the influence of different degrees of light, tempera- 

 ture, moisture and the character of the soil on which they grow. 

 It would not accord with the design of this work to follow him 

 in all of his observations, which cover about 50 pages. Scyto- 

 nema Hoffmanni, Ag. , is one of the plants which received special 



