6 



" omnia ex ovo"-is now fo univerfally received 2S an axiom, that few naturalifU 

 will be likely to accede to their opinion. In fome Conferva, indeed, no mode 

 of propagation has hitherto been difcovered, except by an elongation or ex- 

 panfion, and viviparous diviaon of the filament ; but analogy induces me to 

 fufpe£t that even thefe are alfo propagated by feeds, as has been afcertained to 

 be the cafe in moft of the other fpecies. 



Of the extent of this tribe I feel myfelf unable to offer a conjecture : more 

 than two hundred different fpecies have been already afcertained in the few- 

 parts of Europe in which the Conferva have been at all examined, and I have 

 no doubt but that even our own Iflands will be found to produce a ft i 1 1 larger 

 number. In my Synopfts I have been obliged to omit feveral fpecies, with fpeci- 

 mens of which I have been favored by my friends, becaufe the latter are fo 

 imperfeft, or have furfered fo much change from drying, that it is impoffible 

 to obtain their diftinguifhing characters. In addition to the fpecies which have 

 fallen under my own obfervation, or of which fuch drawings or defcriptions 

 have been published as to leave no doubt of their identity, I have admitted only 

 'thofe of which I ptffefs either (ketches or fpecimens, fufhciently perfect to afford 

 a tolerably correct idea of the recent plant. The accuracy, however, of all 

 defcriptions of Conferva, which are taken from dried fpecimens, for reafons 

 affigned in the preface to my firfc Falciculus, may be doubted, and I therefore, 

 whenever this has been the cafe, have prefixed an afterifk to the name of the- 

 fpecies, in order that a proper allowance may be made. 



The Conferva, by the large quantity of oxygen that they give out, have been 

 thought to render the air about ftagnant waters more wholefome ; but of their 

 ufe and economy no more is yet known than of their number. Many fpecies 

 remain of whofe whole phyfiology we are intirely ignorant, and perhaps no 

 other tribe can be found which ftill offers fo wide a field for difcovery. 



Of thofe who have attempted a divifion of the Confervre into Genera, Dr. 

 Roth and M. Vaucher are the authors who deferve particular attention, and I 

 ihall now proceed to give a fketch of their different arrangements. 



