Xvi FRESH-WATER ALG^ OF THE UNITED STATES. 



individual plants from their earliest germination through their 

 cycles of transformation to full maturity. They relate mostly 

 to snatches of observation, but all tending to illustrate the poly- 

 morphic features of Fresh-water Algae, and the relation of 

 unicellular forms to the fully developed filamentous algae. There 

 is no such thing as the changing of plants from one generic 

 character to that of another. What we do see approaching the 

 appearance of such transformation is simply an undeveloped 

 condition changing to another condition before reaching maturity. 



Dr. Hansgirg, of the Eoyal University of Prague, one of the 

 latest observers noted above, who for five years has been gather- 

 ing specimens in all parts of Bohemia, and made them a study 

 at all seasons of the year, giving special attention to their process 

 of development, sums up his observations in the following seven 

 theses^freely translated from the German. 



We may remark in advance, they are full of valuable hints, 

 but need, in some instances, verification in as far as they relate 

 to our species. 



THESIS I. Most of the Schizophyceae (Cyanophyceae), if not 

 all, are polymorphic algae, which, in different stages of growth 

 in the open air, assume unicellular vegetative forms, and often 

 retain these forms through many generations, but their genetic 

 relation may be readily traced. 



THESIS II. Most, if not all, of the forms hitherto classed with 

 Chroococcaceae, as the genera Chroococcus, ^Taeg., Gloeocapsa 

 (Kg) Naeg, Aphanocapsa, Naeg., Synechococcus, Naeg., Gloeo- 

 thece, Naeg., Aphanothece, Naeg., and others, have a genetic 

 connection with other more highly developed forms, that is, the 

 most (if not all) of the so-called unicellular, aeruginous algae 

 forms have their origin in, or result from, the decay, or separa- 

 tion and dividing of cells of filamentous Schizophycece. 



THESIS III. Such genera of the Family Oscillariaceae Eab. , as 

 Leptothrix Kg., Hypheothrix Kg., Spirulina Lk., Oscillaria 

 Bosc., Phormidium Kg., .Chthonoblastus Kg., Lyngbya Ag., 

 .Hydrocoleum Kg., Symploca Kg., Schizothrix Kg., and others, 

 are often found intermingled with thinner and thicker filaments 

 which are merely younger or older conditions of the same plant ; 

 among them are also forms of the families, Nostochaceae Eab., 

 and Chroococcaceae Eab., and forms of the Family Eivulariaceae 

 Eab.; (Calotricheae Thr.,) ScytonemaceaeEab., and Sirosiphonia- 

 ceae Eab., all of which are genetically connected. 



THESIS IV. The genera Nostoc Yauch., Anabaena Bory., 

 Cylindrospermum Kg., Sphaerozyga Ag., and others of the 

 Family Nostochaceae Eab., embrace many heterogeneous algae 



