16 W. Hofraeister on the Propagation 



the formation of a septum taking place in cell-division, while in 

 conjugation the protruding part of the young membrane con- 

 tinues to enlarge outwards without, in many cases, any sepa- 

 ration of the contents into two halves taking place. The younger 

 innermost layer of membrane remains with that portion lining 

 the old cell-coat, sticking wholly in this in Hyalotheca, Bamhu- 

 sina, Cosmarium. But even in individuals of species of the last 

 genus it sometimes occurs, in Tetmemorus, Closterium (e. g. C 

 acutum, fig. 10), as a rule (although by no means without 

 exception), that the ends of the connected inner coats of the 

 conjugating cells draw themselves out of the cast-off shells of the 

 mother-cells, in extreme cases entirely; so that the cell ori- 

 ginating by the blending of the internal coats of two indi- 

 viduals (inside which the spore is formed) becomes capable of 

 being rounded-off into a sphere. 



Both the cell-division and the preparation for conjugation of 

 Zygnemese are distinguished from the processes in Desmidiese, 

 by the circumstance, that in the former the wall of the oldest 

 cells grows in its entire mass, and does not allow the younger 

 layers of membrane to protrude through fissures or slits. 



In the Diatomese, lastly, the division into two, like the con- 

 jugation, takes place, seemingly in all cases, through and after 

 a preparatory contraction of the contents or separate portions of 

 the contents of the cells ; and in not a few cases the conjuga- 

 tion takes place during, and is accompanied by, division of the 

 contracted contents into two portions. What import for the 

 life of the species has the conjugation of the Zygnemese, Desmi- 

 diese, Palmellese {Palmogloea), and Desmidiese ? Our knowledge 

 of the race of Algse, so importantly advanced by the labours of 

 Pringsheim and Cohn, should allow a more positive answer to 

 this question than that inquirer*, to whom the study owes most 

 brilliant acquisitions, is inclined to give. The idea of sexuality 

 of the lower Algse depends principally upon the perfectly justi- 

 fiable but still only analogical conclusions, which, starting from the 

 observations made during a century on the Phanerogamia, have 

 advanced, through the intermediation of those less numerous on 

 theVascularCryptogamia and Muscinese, and the facts established 

 in Fucus by experiment of artificial separation or union of the 

 sexes, to the CEdogonia, Vaucheria, Sphceroplea and Volvox. 

 Pringsheim's declaration, that physiological questions of such 

 kind as the necessity of the action of the fecundating matter in 

 generation can only be certainly decided by the observation of 

 morphological processes, — will not be adopted. Experiment has 

 long ago proved the existence of sexes in the Phanerogamia, 



* Pringsheim zur Kritik u. Geschichte der Unt. ueber Algen-geschi. 

 Berlin, 1857, p. 15. 



