THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[SECOND SERIES.] 

 No. 104. AUGUST 1856. 



IX. — On the Development and Propagation of Sphaeroplea 

 aunulina. By Dr. Ferdinand Cohn*. 



Up to last year there were few botanists who behcved in the 

 sexuality of the Algffi. Thuret's observations on the antheridia 

 of the Fucacese did indeed open a new prospect, in demonstrating 

 the impregnation of the reproductive spores by minute sponta- 

 neously-moving spermatozoids [antherozoids, Thuret) ; yet this 

 discovery, so long as it remained isolated, appeared rather to 

 remove the Fucacese from the class of Algse, just as the pre- 

 viously discovered sexuality of the Charaeese has altered the 

 position of those plants in many systems. The observations of 

 Pringsheimf, laid before the Academy in March last, have 

 proved that one of our freshwater unicellular Algse also possesses 

 separate sexual organs. Having discovered spermatozoa in the 

 ''horns" (previously suspected to be antheridia) of Vaucheria, 

 and traced their entrance into the orifice of the sporangial cell, 

 IVingshcim has established the fertilizing process in the most 

 remarkable manner, and grounded upon this the conjecture that 

 difference of sexes exists in all the rest of the Alga, and that the 

 resting-spores, the time reproductive organs of these plants, are 

 in all cases impregnated by spermatozoa and are not ca])ablc of 

 germination without this. The history of development which I 

 am about to sketch in the following pages affords new evidence 

 in favour of this proposition : as it rests upon a totally inde- 

 pendent scries of observations, almost simultaneously performed, 

 and reveals most remarkable modifications of this process, it 

 may still lay claim perhaps to an especial interest. 



* Translated from the ' Monatsbericlit ' of the Berlin AcaderaVj Maj" 

 1855, by Arthur Ilenfrey, F.R.S. &c. 



t Annals of Nat. Hist. 2n(l Ser. xv. p.S^fi. 

 Ann. Sf Mag. N. Hist. Ser. 2. VoL xviii. 6 



