INTRODUCTION. 7 



Our knowledge of the life-history of the alga; must make very many advances 

 !M Lire the trui- >\>tein can Ic devclojM'd, and abstinence from adding to the present 

 numerous classitication-, i> an exhibition of self-control not very common. 



There are, lio\\. \,T, certain great groups, which are already plainly foreshadowed, 

 and which no doubt will he prominent points in the perfected classification. 

 Amongst these are the Con^uijattr, or those plants in which sexual reproduction 

 occurs \}\ the union of two similar cells. In the present paper all the plants of 

 this family described are together, since the diatoms are not noticed ; but in Raben- 

 h' list's work the latter plants are very widely separated from their fellows, and this 

 to me the weak point of the Professor's system. 



