XV111 PREFACE. 



Highness the Grand-Duke, the most serene Rector of 

 our High School, conferred the Prorectorate upon me, I 

 determined to make this subject, which appeared both 

 capable of a profound treatment and of general interest, 

 the basis of the Introductory Programme which, in 

 accordance with the good old custom, the Prorector 

 delivers in honour of the birthday of the exalted Patron 

 and Rector of the High School, our beloved native 

 Prince. The main thoughts were soon arranged, and 

 the outlines traced; the illustrative examples added to 

 the text were to be worked out during the printing of 

 the essay, and the natural history of some of the genera 

 of Algae more particularly remarkable in reference to the 

 subject, (Pediastrum, Characium, Hydrodictyon, As- 

 cidium, Sciadium, Palmoglaa, &c.) was to be given in an 

 appendix. But the storm of the revolution, which broke 

 out in May, and shook our blessed fatherland to the 

 very foundations of its existence, soon interrupted the 

 incipient labours ; for our High School was threatened 

 by the tempestuous waves, and it was at the cost of care 

 and severe effort alone, that the threads of scientific activity 

 were protected from total disruption in the midst of 

 the session. But, in the ever- memorable days of July, 

 when the fermenting elements of social dissolution, which 

 we at length saw gathered within our walls, had vanished 

 before the helpful Brother-hand, strong in the spirit of 

 order, like the shades of night before the sun's light ; 

 when in the following month our beloved ruler was 

 enabled to return to his blinded people, who, ungrateful 

 for his beneficence, had risen in opposition to him ; the 

 season was too far advanced, for the projected discourse 

 to be properly carried out in time, on the basis which 



